Running Kalyway 10.5.2

With...

nForce 680i SLI mobo (only one graphics card)
Core 2 Duo 2.66ghz (no OC)
Nvidia 7900 gs
2 HD's one with an xp install one with OSX
4gigs of ram

Kalyway 10.5.2 runs fairly well for most things but many processes (pretty much anything that takes a while is likely to cause crashing).

examples:

-dowloading large files
-importing to imovie
-copying large files from external HD's or Flash Drives

and others...

The system runs with apparently perfect stability if I boot w. cpus=1 maxmen=2048

Anyone have a clue what fix(s) would allow me to run the system with both cpu's and all of my ram?