4Gig DDR2 with VISTA Ultimate 32bit

Hello,
I have just bought a new motherboard from BioStar-the GF7050V-M7. It only has two memory slots and takes a max of 4 Gigs ram. So I decided to top it ip.
I am currently running Vista Ultimate 32bit. My problem is that it reads the 4gigs ram on the startup and gets into windows pretty fast. It then goes into a blue screen and windows shutsdown and restarts.
Now, I have read that the 32bit only uses 3.2gigs of the 4gig ram. I took it back to the shop that I bought the Mainboard and the ram, we tried only 3 gigs and it worked perfectly! The slots on the mainboard work fine and the ram is good.

I will not settle for only 3gigs though!

What is the solution to this problem? Could it be that I need Vista 64bit?