So many Afghan rulers have been assassinated inside their palace walls that one former king, Abdur Rehman, used to hire tasters to test his tea. President Hamid Karzai has the modern-day equivalent: strapping American bodyguards with M-16s, AK-47s and night-vision goggles. From praying in the palace mosque to dining with his wife, wherever he goes the way is first cleared by these men. For his first year they were US special forces; now they are private security (mostly ex-special forces) paid for by the US State Department.

Tanks guard the gateways to the Arg compound. A combination of palaces, arsenal and treasury, it is, like most of Afghanistan, partly in ruins. Entry is permitted only after a series of radio messages and inspection by sniffer dogs. Inside, as workmen dig up the bones of Daoud's family, I can almost sense the ghosts of slaughtered inhabitants. The most recent murder was the most grisly. When the Taliban captured the city in 1997 they took the former president Najibullah back to the Arg, castrated him in his former bedroom, tied him to a Toyota Land Cruiser and dragged him round the grounds before hanging him from a traffic island.

'The land of the unruly' was King Abdur Rehman's description more than 100 years ago of his realm of rocks, mountains and warring tribes at the crossroads of central Asia. It has always been a risky place to govern. Throw in several million Kalashnikovs and rocket launchers, the probable presence of Osama Bin Laden, many of his senior Al-Qaeda lieutenants, the Taliban leader Mullah Omar and the warlord Gulbuddin Hekmatyar, and it becomes the most dangerous job on Earth. In Karzai's 18 months of office, he has narrowly escaped three assassination attempts; his deputy and one minister have been killed. Bombings and grenade attacks occur almost daily in Kabul despite the 4,000 foreign troops there; much of the rest of the country is ruled by hostile warlords and considered no-go areas by the UN and aid agencies. Karzai's own cabinet is full of people who would like him out of the way, and one of his top ambassadors refers to him disparagingly as 'the American puppet'. Apart from overseas trips, he has only once travelled outside the mountain-ringed capital since September, when his motorcade was ambushed as he attended his brother's wedding in their home town, Kandahar.

The man they call the prisoner of Kabul chuckles when I ask how he likes this life. 'I don't enjoy being president at all,' he says. 'It's all hard work and no fun. But I see it as a continuation of the struggle that I have dedicated myself to from the days of the Soviet occupation, right through the infighting of the mujaheddin and the evils of the Taliban regime. What I'd really like is to be able to go for walks, meet friends, drive on Afghan highways, picnic in orchards. I can't do any of these things.' At 46, Karzai is part of a generation who gave their youth to jihad in a country that saw 23 years of war, starting with the Soviet invasion in 1979. Many, like him, forsook a privileged life to join the romantic struggle of turban- and sandal-clad men from the mountains against the tanks and helicopter gunships of one of the world's most powerful armies. Once dashing warriors - as Karzai was when I first got to know him - today they are generally potbellied, bald and bespectacled. Most are bitter too, having watched a successful fight to oust a superpower degenerate into infighting between guerrilla factions that left Kabul in ruins and paved the way for the Taliban.

A keen walker, Karzai has avoided the potbelly, but his beard is thickly speckled with white, and his vision of Afghanistan is a romanticised place that he remembers from growing up as one of six sons of the chief of the Popolzai, one of the royal tribes and direct descendants of Ahmat Shah Abdali, the country's first king. 'Don't you remember the man with the blanket in the orchards of Arghandab, which he opened and it was full of delicious pomegranates?' he said, recalling a trip to Kandahar on which I accompanied him in 1988. One reason I had gone was his rhapsodising about its 40 varieties of grapes and pomegranates so sweet that poets wrote elegies to them.

Instead, what I mostly remember is the constant bombardment by Soviet helicopters.Today the notion of picnicking in the orchards seems absurd. Snow on the peaks of the Hindu Kush provides a picture-postcard backdrop, but wherever there is open land, chalked skulls-and-crossbones warn of landmines. The orchards dried up long ago; the Russians bombed irrigation channels to stop them being used as guerrilla hide-outs, and there's been a five-year drought. There are no decent roads. Karzai's family house in Kabul is in ruins. As for the beautiful girls he remembers from his youth, most Afghan women are still shrouded under burkas, fearful of reprisals from fundamentalists if they show their faces.

Yet Karzai's passion for his country makes it hard not to warm to him. Unfailingly courteous, he speaks in an old-fashioned English, refined in the old Anglo-Indian hill station of Simla, where he studied, talking of 'miscreants' and addressing female visitors as 'ma'am'. He has a fondness for mirrors, keeping one on his office wall to adjust his astrakhan hat and chapan, the long stripy silk coat that has become his trademark, prompting Tom Ford of Gucci to describe him as 'the chicest man on the planet'. It's a description that never fails to amuse him: he used to live in jeans and a leather jacket. 'I only ever put on the chapan because when I arrived here in Kabul in December 2001 it was very cold and I had left all my clothes in Pakistan. When I started wearing it, the girls in Kabul went mad, particularly my female ministers. They told me it looked stupid and too conservative. Yet now everyone I meet asks about them. The first thing the Chinese premier said to me was that he wants one.'

Now he has a whole wardrobe of chapans in different colours and linings, some with fur, and his own full-time tailor in the Arg. But there seem few other perks. The palace is draughty and suffers the same power cuts as the rest of Kabul. Gifts from foreign dignitaries are all handed over to the state, much to the irritation of Karzai's wife, Zeenat; he forced her to hand over a diamond ring sent by a Gulf-state ruler. Most visitors come out feeling sorry for him, trapped in his drab office, drinking endless cups of green tea with endless tribal delegations and dipping into small glass dishes of dried almonds and raisins from his beloved Kandahar, to which he can no longer travel. 'I'm here in this office from 8.30am to 8.30pm every day, seven days a week,' he moans. 'Even when I'm at home there are always people to see.' One person he meets every day is the former king, whose cause he once espoused. 'His Majesty ruled this country for 40 years. He knows it better than anybody.' Others say he visits out of guilt, having connived with the Americans a year ago at the loya jirga, or traditional tribal assembly, to ensure the monarchy wasn't restored.

Karzai's biggest challenge is not the long hours, or even lack of security, but the fact that almost nobody in Afghanistan takes any notice of him. When he sacked the interior minister last year, the minister set up roadblocks to prevent his replacement arriving. Karzai passes laws ensuring press freedom - and ministers send police or army officers to deliver death threats or arrest journalists who criticise them. He lifted the Taliban's ban on music and satellite television, only for his own judges to reintroduce it. Warlords such as Ismael Khan in the west collect border taxes and customs duties and refuse to pass them on. Even Karzai's wife ignores his wishes. 'When I go home she doesn't let me choose the television channel,' he laughs. 'She insists we watch news all the time.'

Karzai is often referred to derisorily as the mayor of Kabul. Yet somehow in the next six months he is supposed to come up with a new constitution, and in a year's time hold elections in which he would clearly like to be elected, though he admits: 'If anyone had told me I would be president one day, I would have thought them mad.'

Eloquent and gifted at languages, he had a youthful ambition to be a diplomat, maybe one day foreign minister. These plans were brought to an abrupt end on Boxing Day, 1979, in Simla, where he was doing a master's degree in politics.

'I was walking from my dormitory to my college when I passed two girls walking in the opposite direction,' he recalled. 'They were talking about the Soviets invading Afghanistan. It was a huge shock, the loss of sovereignty of my country, and I became determined to fight.'