Vista 32 is capped to "seeing" 3.2Gb of RAM. More than that just doesn't show up.
Complete rubbish, i recently built a Vista 32bit system with 2x2gigs and it see's 3.5gig ram, this system using a 2180 at 3.3ghz is faster than a 6300 at the same speed but on 32bit XP with 2x1gig ram.
Read the article on here somewhere showing that a 32bit Vista with 4gig ram is faster than 64bit Vista.