Since 32bit can create over 4G combinations, it theoretically should read 4G memory easily, but as I understand it some of the capacity is taken up by ROM, other drives, etc so there is only around 3G for RAM.
Also I've read most programs only are allowed 2G of RAM, which would mean any gains with another 1G would be minor?
The program that is giving me the most trouble is Premiere Pro CS2, I suppose that one only uses 2G.