Well, after fighting with my motherboard, ram, power supply and bios for two long weeks, I finally determined that the problem was, in fact, the CPU itself. I had a defective AMD Athlon 4400+ X2. This being my first AMD box, I had no spare to swap in its place to verify it worked. I ended up purchasing a second power supply, using the ram out of my old computer, heck I even switched keyboards thinking it could be some freaky effect of my ancient Kinesis Essential. Once I had essentially a brand new system with a different power supply, different memory and a different motherboard that exhibited the exact same symptoms, I knew it had to be the CPU.
This is probably the biggest benefit of going with an integrated system--they're less likely to suffer from a single fault that becomes very difficult to diagnose. Having planned on going SLI, at least I had two video cards to work with while trying to fix it.