the ram is being used up by other peripherials, mostly video card. unless you use xp x64 or vista x64, you'll never see the full amount. as for the processor, it could be power savings. it'll go to 2.4ghz when under load.
Are you using 2x2GB or 4x1GB? The P31 and G31 chipset is limited to using two stick of memory if it's double sided (which almost all memory is nowadays)
The amount of Turbocache memory may be configurable in the BIOS, I'm not sure. Either way, Turbocache is completely pointless for a card like the 8600GT with dedicated memory onboard.