[Omega]

I've never had any personal success with this solving problems, but try pulling out your SB Live and cleaning out the drivers/registry stuff from it.  Many people will say it's the root of nearly all problems, and I'm not going to tell them it's not, simply because I don't have a better answer.

NICs can also cause problems, and sometimes will only let a system run stable in one certain position, but I don't think that'd be a problem on your configuration, seeing as how it's on its own IRQ.