There is no direct upgrade path from XP to Win 7.
If you wanted to upgrade from XP to Win 7 and keep all your customizations and installed programs etc. you would need to do an in place upgrade to Vista first.
You would then use the Win 7 upgrade media to upgrade your new Vista install.
The best way to upgrade from XP to Win 7 is a clean install.
That is backup your data and format and install Win 7 to the clean drive\partition.
If you are just trying to see if your hardware can support Win 7 then the Win 7 upgrade advisor suggested by Joe is a logical first step.
This is especially true for older machines\hardware.