When Jürg Lehni was 9 and living in the Swiss city of Lucerne, his older brother was given a Commodore C64 home computer. It was a defining moment in Lehni's life. He became obsessed with the machine, absorbed every detail in the manual and began, when his brother wasn't looking, to make new applications and devise new games for it.

Lehni talked to his maths teacher about his hobby and was given more manuals to read until he was experimenting with highly sophisticated systems far beyond most nine-year-old boys.

Today, 20 years later, Lehni is what one might call a computer software artist and, along with the British graphic designer Alex Rich, is about to open A Recent History of Writing & Drawing, a new show at the ICA. His arts career took off when he abandoned a degree in engineering and, while an undergraduate at the École Cantonale d'art de Lausanne (Écal), he invented a machine called Hektor, a “spray can output device” that has now performed, spraying graffiti-style images on walls, in arts venues all over the world.

“I wanted to make new things with new meanings using what I knew already,” he says. “I wanted to bring back the spirit of printing or publishing or design from the past, but using modern technology. My computers became my working tools, my brushes and paint.”

Rich was a member of the jury that judged Lehni's Écal degree show in 2002; he recognised in Hektor a new tool of communication. “Hektor was a big hit in Japan [where it was displayed in 2006] because the Japanese enjoyed the translation of imagery from mind to machine to wall,” Rich says. “They had their photographs taken and these were turned into drawings on the computer screen, then translated on to the wall with the spray can. They saw Hektor as a character with a distinct personality, as if it were human, while being amazed and baffled by it.”

While Hektor remains something of a celebrity in the specialist world of computer art it is a newcomer, Viktor, also designed by Lehni, who appears in the ICA show. Viktor is a drawing machine made from a mixture of digital and mechanical technologies, most of which were invented for other uses - actually, all the machines on display in the show were constructed from elements plundered from other machines.

During the exhibition, artists, designers, architects and even a shopkeeper will collaborate with Viktor in weekly workshops, instructing the machine to provide an accompaniment to their own performances. For example, Tuomas Toivonen, a Finnish architect and electronic composer, will perform on the Hyalonium, an electronic glass harp, while Viktor creates a collaborative image on a black wall behind him.

“We are all being sold proprietary software all the time and being told how to use it in a prescriptive way,” Lehni says,” but it is possible, if we know how, to bend it to our own will and to use it in a different way. The capacity of this software is not anticipated by us and it often has poetic potential.”

Personally, I struggle to see the poetry in computer software, but Lehni and Rich see it in abundance and they are not alone. The artist Harold Cohen, now 80 years old, built a machine called Aaron in the 1970s, a computer programme capable of autonomously generating original imagery. Its latest works - described by the gallerist Jesse Jacobson as “IBM's Deep Blue meets Jackson Pollock” - go on show in London tonight.

Other exhibits in the ICA show include Dots on Demand, an interactive device that allows visitors to have a short phrase cut from a piece of paper in a simple dot-based typeface. Meanwhile, News on Demand enables visitors to use a hand-held printer to deliver short items of information in a style determined by the user's hand movements.

Is their art in danger of becoming too geeky? “Sometimes we enter territory that is so technical that it can be seen as geeky, but there is also beauty to be seen in these things,” says Rich.

I fear it is more geeky than arty, but perhaps people will engage with Viktor in spite of his unprepossessing appearance. You may be greeted by something resembling a computer demonstration workshop, but pushing buttons is always a pleasure.

A Recent History of Writing & Drawing is at the ICA, SW1 (0207-930 3647; www.ica.org.uk). Harold Cohen is at Bernard Jacobson Gallery, W1 (020-7734 3431)

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