Re: Running memory out of sync with CPU...
Ya, Athlon XP will take a dive if you run the RAM out of sync. You can get better latency and bandwidth with some chipsets in sync vs. even a higher RAM clock.
nForce is particularly weird cuz its "dual channel" isn't really quite such at all. The 3 DIMM dealie is a major clue-in. It is by far the fastest if you keep the RAM clock and CPU FSB in sync. The chipset has 3 memory controllers. It is designed to be really great for an IGP, cuz the IGP can have its own controller or two, basically, I believe. For the CPU, it's not as useful (especially cuz the FSB isn't able to take advantage of dual channel bandwidth anyway).
Some of the later VIA chipsets, on the other hand, are ok with a higher-than-FSB RAM clock. I believe this is caused by some buffering prefetch mechanism in the chipset that can take advantage of the lower latency and higher bandwidth RAM.