Good, sound advice here:
http://www.tomshardware.com/2008/02/15/vista_workshop/page5.html

[quote:cc66d537a3]... it doesn't make sense to install a 64-bit version of Vista in order to better utilize 4 GB of memory simply because the 32 bit version would only recognize 3.5 GB. The problem is that while it is true that you would &quot;gain&quot; the missing memory, you would also immediately lose it to the system due to the 64-bit version's larger memory footprint. Thus, using a 64-bit version really only makes sense with larger memory sizes.[/quote:cc66d537a3]