The company most people use to search the internet wants to be the company that delivers your TV programmes - and sells the adverts to run alongside them. That's Google, which has announced the launch of Google TV, hoping to marry the technology of television with the internet.

It wants to turn your TV set - or the set-top box above it - into a computer capable of turning web video into a TV signal so that you can range across the internet.

"We've been waiting a long, long time for this day," Eric Schmidt, the chief executive of Google, told the Google I/O conference in San Francisco, where the company was showing off its latest technology offerings. "It took a lot to make this happen."

In particular, it needed "extraordinarily fast" computer processors that had just become available, he said. But he admitted: "It's much harder to link up a 50-year-old technology and a brand new technology than those of us from the brand new technology thought."

There are plenty of examples of companies trying to marry the internet to TV but ending with them as divorced as ever. Microsoft has tried twice, with WebTV and its mildly successful Media Center. Apple has AppleTV, a set-top box that even Steve Jobs dismisses as "a hobby". Then there's Joost (which discontinued its application last year), Yahoo Connected Life, Digeo and Intel's Viiv. None has penetrated the public consciousness.

Google insists it can work: "Imagine turning on the TV and getting all the channels and shows you normally watch and all of the websites you browse all day - including your favourite video, music and photo sites," it says in a Googleblog post. "We're excited to announce that we've done just that ... Want to check out that funny YouTube video on your 48-inch screen? It's just a quick search away."

Despite appearances from Sony and Logitech, the first products are not expected until later this year - and some analysts think Google may be aiming for one of the net's "zero-billion dollar markets".

"The road to interactive TV is littered with failures, mainly because people never get the user experience right," said Alx Klive, chief executive of WorldTV.com, who has been in the field of "internet television" since 1995. "Too many companies don't understand the difference between sitting in front of a laptop, and sitting 10ft away from a TV. It's very hard to change people's habits: we've been watching TV in pretty much the same way for 60 years."

All that has changed, he suggests, is the addition of remote controls and, more recently, hard drive devices such as Sky+ and TiVo, which store the programme as a digital file so you can pause and rewind programs.

The key problem, said Klive, was finding enough content on the web to fill an evening. "What we've found is that on average if people can't find something that's at least 40 minutes long online, they won't bother," he said.

But James Governor, of RedMonk Consulting in Maine, said Google was on to a winner. "We are going to get integrated internet TV. I think that the integration of data-driven sports experiences will drive this in the US - where statistics matter so much for baseball, rather like statistics do for cricket here."

But there's another worry: if your TV becomes a computer, what happens when it crashes, its software is corrupted during an update, or it is attacked by malware? Though the latter risk remains unknown until the products are available, Kline said the second problem had already affected a Blu-ray DVD player bought in the US.

Governorsaid crashing was not a problem. "Anyone who's got a Virgin Media or Sky box knows what it's like to have to unplug them and restart them. It's really not a big deal."