Home Premium to Ultimate

I purchased an upgrade disc directly from Microsoft. I have Vista Home
Premium 32bit. I just started law school and must have Ultimate. When
I install the DVD, the "upgrade" option is grayed out. The message
says, the version on the laptop is newer than the DVD installation.

I have SP2 (which I just installed a few days ago, thinking that might
solve the problem). It didn't.

How can I install the upgrade? Help!