Technology gurus sell the Internet as a vast electronic mirror on the real world, where anyone can browse in shops, bank their money or take language lessons. But for all the rhetoric, the Internet is a distinctly middle-class neighbourhood, and one part of town remains conspicuously absent - the slums.

That's a situation two Irishwomen set about changing four months ago when they dropped lucrative careers in Europe to come to Africa and put one of its worst slums on the Internet map.

Emer Cronin (30) and Fiona Whelan (31) arrived at the notorious Mathare Valley slum in the Kenyan capital, Nairobi, in January. They brought six computers, two printers, one scanner and a host of pioneering ideas to bring the Internet revolution to local teenagers.

After going through a youth club, the women began an intensive project to get a group of 20 school-leavers online. Many of them had never seen a computer when they began.

Now the teenagers from Mathare are fully qualified cyber-citizens. They can whizz their way around complicated graphics programmes; have set up their own Website with the help of a group of Dutch teenagers (www.nairobits.org) and have opened an exhibition at the city museum.

Some now want to make a career out of the Internet. Geoffrey Otieno (20) is good at art but had no outlet for his talents. Now he has set his sights on becoming a Web designer. "Before this I only knew what a computer looked like, but had never touched one", he says, scrolling down through his own Web page.

In the beginning, the idea seemed rather fanciful. Emer Cronin had left Dublin for a successful career as a Website designer in Amsterdam, where her working name is Emer Beamer. One evening, watching yet another depressing news item about Africa on television, she decided it was time to put her skills to a new use.

"We were being force-fed African disaster stories through the media. I was sure there must be better human stories to be told out here," she says.

Her original idea - to travel Africa and post stories and photos on the Internet using a laptop - was quickly dropped because it was a "typical white-black relationship," she says.

"We decided the solution was to let people here put up their own content."

Emer persuaded her friend and neighbour, Fiona Whelan, a theatre set-designer and teacher from Lucan, to join the adventure. A third person, Hester Ezra, a Dutch public relations professional, also signed up and they started pitching for sponsorship. It wasn't easy.

"A lot of the people we approached for funding thought we were nuts. They were thinking: street kids, must be sniffing glue, why bother?" says Fiona.

Nevertheless they persisted, cadging favours from friends and funding the project out of their own pockets. They bought six second-hand Apple Macintosh computers from a design company (Apple turned down a sponsorship request) and got some sponsorship from the Dutch embassy.

But even as they touched down at Nairobi's Jomo Kenyatta Airport in January with computer leads stuffed in their pockets, it was still touch and go. "Getting off the plane we didn't have enough money and didn't even know if the youths were ready for the programme. Of course, we didn't tell our sponsors that," laughs Emer.

The only sure thing was that they were headed for Mathare, a notorious slum that has become a by-word for the chronic failure of African urbanisation.

Mathare is a vast city of rough shacks where 100,000 people live in cramped, squalid conditions. Raw sewage streams through the streets and AIDS, crime and drug abuse are endemic.

Emer and Fiona made contact with the Mathare Youth Sports Association (MYSA), an innovative organisation founded by a Canadian philanthropist more than 20 years ago which provides structure and hope to youngsters who have little of either. MYSA picked a group of 20 students, mainly boys, and within weeks the Nairobits project was operating.

It was slow in the beginning. A television set is a luxury in Mathare so computers were an alien concept to most of the students. "They had never touched a keyboard and didn't even know how much force to use to push the floppy disks in," says Emer. "We made up a rap to teach them how to click and double-click the mouse."

The students were so quiet at first, "we weren't sure if we were getting through". Then, one day, the penny dropped. "We couldn't get them to take lunch-breaks," says Fiona. "They would grab keyboards that weren't even hooked up and start poring over the keys, like you would practise the piano on a tabletop at home."

Within weeks the teenagers were mastering complex design programmes such as Adobe Photoshop and had started to build a Website. But the project wasn't just about pushing buttons. An equal emphasis was placed on coming up with a creative Website content, which was directed by Fiona. "There was no point in them having this wonderful Web technique if they didn't have something to say," she says.

Drawing, photography and acting were used as conduits for ideas that were then transformed into photos, animations and stories for the Website. The themes were rooted in the tough urban environment of Nairobi - drugs, poverty, the chasm between rich and poor in Kenya. One boy, John Kiarie, took a picture of a boy sniffing glue, which is posted on his Web page.

Unlike most "white" Western Internet sites, the content is not highly polished, with flashy graphics and intricate drawings. "Since they came from a football organisation, we weren't expecting them to have great art skills. But early on they realised that it didn't have to a brilliant drawing to be a successful one," says Fiona.

The centrepiece of the Website is a virtual "island", built across the Internet with the help of teenagers 4,000 miles away in a Dutch secondary school. Communicating through an online chat room designed by Emer, the two sets of students swapped ideas about what they would put on the island.

The differences in approach were instructive. The Dutch built airports, department stores and discos; the Kenyans built houses for each other. There was also some confusion over the Dutch coffee shop. "They were selling hash, but our kids didn't realise it. They just thought that drinking coffee was a nice idea," says Emer.

The £60,000 project was an example to the bloated bureaucracies of the hundreds of aid agencies based in Nairobi. The two Irishwomen flew on budget flights; worked for free; rented an unfurnished house; and worked with second-hand equipment. Before finding a premises, the project was co-ordinated from public phones in Mathare.

While aid-agency workers spin around in Land-Rovers, the women's only transport was a £50 bicycle and the cheap but dangerous matatu public buses. Just two weeks into the project Emer fractured a leg while getting out of a matatu and spent the rest of her time on crutches. They also had to adjust to the slower pace of life in Africa.

"In the beginning we were more stressed by the difficulties," says Emer. "But people aren't sitting under a tree and saying everything will be OK tomorrow. People work at things very hard, but even then they still don't always happen," says Emer.

They were also surprised at the proliferation of small corner shops with e-mail facilities. Emer has discovered more than 100 during her stay. But the Internet does not have the same potential for change as in the West, Emer says.

"Before, I had this romantic idea that they could skip the industrial age and go straight into cyberspace. But now I feel it's more that the gap will widen if they don't get with it soon."

For the Nairobits children, though, the project has opened up a world of possibility they never knew existed. While Emer and Fiona are flying back to the Netherlands this weekend to restart their careers, the project will continue.

There will be weekly workshops from local Internet specialists until the end of the year, and some students have obtained work placements from local companies.

Earlier, there were fears that the students, none of whom has computers, might get disillusioned after the project.

"We were afraid we might open a door that would then slam shut," says Fiona. Any such doubts have evaporated.

"The Internet is incredible," says 18-year-old Josses Karani. "It's like having the whole world in one box."