Although I'm against Vista, Ultimate is the best version of
Vista. A lot can be done with it as there aren't as much
restrictions as the other versions.
One important question to consider when downgrading:
Do you have problems using it?
I noticed you mentioned that it will be for use in university. Are
they using VPN? Is the VPN supported by Vista? Or rather, does the
school support Vista?
There are certain things which schools do and we can't tweak. If
the school supports Vista, most likely they will have support for
Vista as well and we can't go about downgrading lest it goes
against certain policies.
You have to check that out. If you still want an XP, I would
recommend dual booting, that means having two operating systems (XP
and Vista) on the same hard disk.