[this_is_gav]

Home Premium will have everything you'll likely need (so long as you don't have to log onto a Windows Server domain, which is highly unlikely in a home system).

Get the laptop and try putting the serial number into Microsoft's media ordering system - you might be able to get 64-bit media for a couple of quid (delivery only), though it can take a couple of weeks.

Many OEMs aren't supplying 64-bit media as standard as it can be a bit picky if you don't know what you're doing regarding things like codecs (DivX need to pull their finger out...) and so on. You're unlikely to run into problems, but they do happen, and you'd have to look a little further for support.