It is possible to work around the Windows XP to Windows 7 upgrade issue if you have, or can borrow a copy of Windows Vista. It doesn’t even have to be licensed since you won’t be activating it and won’t have it loaded for more than a few hours — well within the 30-day trial period. Just upgrade from Windows XP to Windows Vista, and then upgrade the newly installed Windows Vista system to Windows 7.
There is no guarantee that this will go off without a hitch, but is probably much easier than doing a clean install, which is recommended by Microsoft and most experts.