More ram is cheap upgrade, and most (but not all) mem is cheap now. 2g is pretty fair, until ya get into advanced graphics, sound manipulation, autocad etc.; so the answer partially depends on use. And that then goes for graphics card too. More memory there, means less memory borrowed from main memory pool, leaving more mem for other processes... This is sometimes why you know you have 2gig mem installed and only seey 1.5 etc., the graphics are 'borrowing' rest.
32bit os will only address 4g(2 to the 32nd) mem, even if sys will physically hold more though. There is a work around(for gamers etc.), but then compatability problems for some programs and hardware. 64bit can address more mem too(2 to the 64th or 16 terabyes-which the machine physically won't hold), but it has compatability problems too.
If ya get focused on 1 or a few models; go to their sites and check their forums on that model. Or just put that model and 'forum' in a google search. There are passionate, inside computer people that can rattle off models and inherent weaknesses, just like tree workers! In fact for a lot of general searching, i'll put term(s) and the word 'forum' in a google search. There are people offering free help in almost every endeavor.
The word 'laptop' is a lil'touchy. These systems fight heat, and any, soft surface(lap, bed etc.) they sit on can potentially block ventilation. Also, with all the exploding batteries in the past, recomending or using terms that inherently recomend placing sys on lap has become a rather large potential liability...
Vista is more of a resource hog and has some compatabilty problems too. Office 2007 has .docx(xml based) instead of .doc files, and is totally changed interface, has compatablility problems(there is a free compatability upgrade for previous office users to read these files). Would only get it if i had too, once again, ask at target school, if office2007 is what everything is set up for though... There are real deals on educational software, and don't overlook office ultimate educational discount if shopping.