You can't upgrade from XP to windows 7 as such. the upgrade version will work but it would make you do a clean install and wipe your hard drive and clear everything from it. (the same as a full version would).... the upgrade from XP to windows7 is basically just a license upgrade to save you a bit of money.
There is no guarantee that a computer designed to run windows XP would run windows7 either, there may be problems with some of the hardware not having any drivers available for windows7 and the computer also may just not be powerful enough to run windows7 happily.
You can download and run the windows 7 upgrade advisor from microsoft and it should tell you if your computer would be able to run windows7 or not.
http://www.microsoft....en/details.aspx?id=20