OP, why don't you try a 1GB DDR2 800MHz RAM to see if the system works with 2GB+1GB+1GBvRAM.
But IMO there is no link of vRAM and RAM, the total expandable memory of a system is the max amount of RAM one can use, w/o the VRAM and not RAM+VRAM.
BTW, is that CM eXtreme PSU working fine till now??