License help...will this devious plan work?

Okay, so my current computer has Windows XP Professional. I want to keep XP, but set up a dual boot with Windows Vista Ultimate. Here is where the devious plan begins. I was able to get my hands on a 32bit Windows Vista Ultimate "upgrade" disc at the affordable student price of $13.00. However I am under the impression if I use my upgrade vista to install a dual boot it will deactivate my XP license - which i don't want if I want to dual boot. Unfortunately my university doesn't offer the full windows vista ultimate. So I'm planning on picking up an additional copy of Windows XP Professional at the student discount price of $4.00 and using that new license during the Windows Vista activation process. Allowing me to keep my old windows xp active and dual boot to vista ultimate. will this work? what do you guys think?

It wil work. Just be sure to give the second install a different name to avoid confusion in the boot loader.
Also search around because you can do a full install from Vista upgrade.
I cant remember exactly how but it can be done.
It concerns a command line switch.