Are you booting off the disk?
I seem to remember that the upgrade option is either only available from booting off the disk, or only available from running the installer in Windows XP. I don't remember which one it is.
But you don't want vista anyway
... Inventor and many other programs have problems. As Pavan suggested, a dual boot might be the solution for you. To partition your drive without formatting, check out Partition Magic (its 70 bux.... but probably worth it (
http://www.symantec.com/home_homeoff...sp&pvid=pm80)). You can either install vista on a split drive, or sell your key. It's up to you.
Jacob