The corporation has agreed a deal with wi-fi firm The Cloud, which operates 7,500 hotspots around the country.
The news website, programme sites and downloads of TV shows via the iPlayer can be accessed freely.
The BBC has also confirmed that users of Apple Mac and Linux machines will be able to use its TV catch-up service from the end of the year.
The broadcaster has signed a deal with Adobe to provide Flash video for the whole of the BBC's video services, including a streaming version of its iPlayer.
Currently only Windows XP users can use iPlayer, downloading programmes on to their PC and keeping them for up to 30 days.
The deal with The Cloud was about widening the reach of BBC content, said Ashley Highfield, the BBC's director of Future Media and Technology.
It comes down to cost per person and reach at the end of the day
Ashley Highfield on a download service for Mac and Linux users
Any wi-fi enabled device will be able to surf the BBC's website in one of The Cloud's hotspots without paying a log-in or subscription fee. Users wanting to download a BBC programme - or stream a video - will have to use a laptop initially.
But the BBC said the ambition was to let users download programmes over wi-fi on to portable devices, such as the Sony PSP and Nokia 95.
Mr Highfield said: "This is the first of what I hope will be a number of relationships with wi-fi operators.
"For us the killer is - there is no subscription required. You will be able to consume any of the content on bbc.co.uk; watch an episode of Strictly Come Dancing with your coffee, or if you are pressed for time, download it and watch it later."
At the end of the year users of Windows, Mac or Linux machines will be able to watch streamed versions of their favourite TV programmes inside a web browser, as well as share the video with friends and embed programmes on their own websites, sites such as Facebook and blogs.
Flash is one of the driving forces of online video, with millions of programmes and clips using the format every day to deliver content over the web.
Wi-fi has become increasingly popular
"This is a major step into the Web 2.0 world," Mr Highfield.
Erik Huggers, the BBC's Future Media and Technology Group controller, said the corporation had partnered with Adobe because it was "leading the charge in making sure content is available across a variety of platforms".
But Mr Highfield said the BBC had not committed to offering the iPlayer to Mac and Linux users who want to download and keep content on their machines for a limited period.
He said: "We need to get the streaming service up and look at the ratio of consumption between the services and then we need to look long and hard at whether we build a download service for Mac and Linux
"It comes down to cost per person and reach at the end of the day."
He added: "We are not ruling it out. But we are not committing to it at this stage."
More than 250,000 people are using the iPlayer regularly each week, said Mr Highfield. The corporation is hoping to have more than 500,000 regular users by April 2008.
The BBC has said it hopes to offer high definition (HD) downloads in the not too distant future.
"With spectrum capacity severely limited on Freeview at least until 2012 we believe quite strongly that IP (internet protocol) is a great route to getting HD out to wider audience."
Mr Highfield said the corporation had already started talking to internet service providers (ISPs) about any potential impact of offering HD video content. Earlier this year ISPs expressed concern that the BBC's plans for the iPlayer could hit bandwidth.
Mr Highfield said the BBC was looking into scheduling HD downloads in the night when demands on the net were at their lowest.
He added: "We do not believe there will be an impact on the infrastructure of the UK internet. It is more than capable of dealing with this level of demand."
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