, and welcome to the forums.
You'll more than likely run into compatibility issues regarding your laptop's hardware and trying to run Windows 7. In addition, the upgrade facility it pretty easy to use, so it has not been 'tweaked' yet for folks trying to upgrade from XP (or Vista, for that matter). This is, after all, a pre-Beta - meaning that not all things work.
But, on the other side of the coin, ZDNet is warning more those users who are going to try to upgrade production machines - since this is an old laptop for you, I am sure that you really don't care about it and it will be somewhat of a learning experience for you - and you'll be able to report problems as well.
If it were me, I'd do the exact same thing - backup the HD< then upgrade - and see what breaks.