Shitface, how much ram are you thinking of upgrading to? Because if you're only going up to 4gb, the additional memory support that 64bit offers is pretty much negated by the increased ram use. I'm fairly sure that 32 will acknowledge 3.6GB, whereas 64 will see the full 4GB, but will use an additional 500mb at startup. Skipping the upgrade obviously isn't an ideal solution, but if you're only going to be using 4gb, upgrading your OS to compensate may actually decrease the amount of available ram.

If you're upgrading to anything more than 4gb this obviously becomes a moot point.