The short answer is "yes, but you probably won't be able to use it all"
The long answer has to do with 32bit vs 64bit operating systems and how much of the possible address space is allocated for I/O devices. As far as i know, in winXP 32bit you can use up to ~2.5 GB of memory space and the other ~1.5GB are for I/O devices. Seeing as how the version of vista that you are talking about is still a 32bit OS, there is no reason for this convention to be any different. If you are building a system around 32bit vista, don't bother buying any more than 2GB, if however you already have a 64bit system and have purchased a bunch of ram (in excess of 2GB) and you are wondering whether to go with the 32 or 64bit version to make full use of all your ram, then by all means, buy a 64bit windows vista.