Just to nitpick a lil :P 32bit os can see up to 4 gigs to free up some of the memory when dont see all of it, go into yer bios and reduce the amount of memory that's dedicated to the graphics card. Vista 64 has the same issues but its not gonna matter since yeh can use more then 4 gigs.

One thing I advocate if yer gonna get vista get 64bit version and get at least 8 gigs of ram.