Came across a thread on MoneySupermarket (don't know how good it is, tbh) where someone called the companies that do these deals 'con artists'.
Now, I wouldn't go quite that far, but would be happy to use quotes - it's definitely a "free" laptop... There will surely be some element of what is paid to cover it, else we'd never spend a bean on new laptops, yippeeeeee!
More important, however, for the OP (in case she hesitates to post for a bit) - do please take note that Windows 7 is due out on October 22
That may mean a lot of changes - Windows Vista will be classed as "old hat" - though I don't yet claim to know the effect it will have - whether Vista machines will be sold off cheaply to clear the shelves and make it easy to say "All PCs run Windows 7" (actually that might be difficult, at least to be still selling them in the under 300 pound price bracket, because Windows 7 might be a bit more memory hungry, and not all machines out at present seem capable)... or the firms may simply "split" their products into "Vista" or "Win 7" and have the more up-market machines in the Win 7 section.
So, it may well force some changes on the deals that are available because the market they might be aiming for (students and under-35s?) who are ready to pay a monthly fee for a mobile deal with a laptop in the bundle, and could be "put off" by "out-of-date" Windows Vista.
Now, I hope that's not confusing - it's me speculating, and hopefully they will give just as good deals, with Windows 7 installed, though there might be a slight delay before all the deals include it. However, forewarned is forearmed, and you would do well to check if Windows 7 is installed. If it isn't, then I'd sit tight. Don't even be taken in with "there's a ffree upgrade" as there might be (a) delivery costs and VAT and (b) who is responsible for making it work if the upgrade doesn't go well...
Far safer to get a new machine with it installed from day one, in my view (and not just for those who feel out of depth with technology, believe me, I for one would likely hold on for a new machine with Win 7, and I've been using computers for 30 years).