So I maxed out my K9N2GM motherboard with 8GB of RAM, and noticed that VMware Workstation 5.5 wouldn't see past 4GB even when it was running under XP x64 Edition SP2.
I upgraded to VMware WS 6.5 and now my virtual machines can use over 7GB if I need it. The only issue I had was that my PC would suddenly reboot the first time I ran workstation and player.
If you're looking for an affordable and stable system to run VMware, I suggest reading my upgrade thread here:
http://purefinity.blogspot.com/2009/01/amd-athlon-x2-upgrade.html
I originally bought it more for gaming, but VMware runs great too!