I'm not bothered whether it's Home Premium or Ultimate but it must include SP1 on disk and must be the 64-bit version. It's likely to be used on at least two computers (consecutively) so the retail version at slightly less than twice the price looks like the better deal.
The best I've seen so far is ebuyer at £98.70 delivered for the home premium 'complete package'.
I am a student in higher education so I guess I can get some sort of discount but I haven't seen anything yet.
I tried to search here, but I got overwhelmed by 'computers shipping with vista' deals.