the loss of ram is due to the limitation of 4GB with a 32 bit OS. This memory cap will include memory from the video card. I'm not sure if you can do it in the drivers but I was reading somewhere you can use a tool like Rivatune to disable turbocache. To be honest, I am not sure why turbocache would allocate so much system memory. Try using CPUID or go into the bios to determine if all your memory sticks are recognized.
Switching to a 64 bit OS will give you access to all system memory (minus the allocation from Turbocache).