I have a friend who wants to sell their computer, but obviously all personal information and software that it is on it needs to be removed before doing so.

Usually I would format and reinstall it, but I cannot easily get hold of the required XP DVDs and I'm not 100% sure the serial number is stuck on the case as usual so getting hold of it will probably require more effort than I'm prepared to spend.

So, what's the best and quickest way to remove and uninstall everything from the PC without reinstalling it?

Thanks.

EDITS: I'm looking to remove things like Internet History and all installed programs, too. I know how to remove the history and each individual program, but that could take hours.

The machine is not branded and therefore there is no website I can go to download recovery software. There is no recovery partition on the computer and I'm not aware of any recovery DVDs for it either. I can only assume it was installed from a retail copy, and therefore there is no way to recover it to factory settings.

It needs to have XP installed, not any distribution of Linux. Like most average people, the person getting the computer will not understand what to do with a computer that doesn't have Windows installed, and software like Office does not work on Linux either.

Buying another licence is not really an option either. She has just brought a laptop to replace the computer, so buying another licence for a computer that she's getting rid of doesn't really make sense.

Thanks for all the help so far!