The problem with XP is it's RAM address range limitation, only 3GB, it can 'see' 4GB and list it in the system, but only uses 3GB of it. This problem was fixed in Vista. (so I was told anyway)
Greg

XP will actually use 3.5 GB or RAM. So will Vista - unless you get the 64 bit version! That brings many other problems.

We once spent all evening getting a colleagues Vista64 setup to work with all the required company software (designed for XP 32 bit). After getting various weird 64bit versions of components and doing required work-arounds, we had it! Then came the bummer - the VPN client was not supported on Vista64! All that work down the tubes for nothing!

Dusty