Higher rated RAM almost always 'works' with motherboards which are specified to 'work' with lower rated modules. It will simply be operated at the lower speed, which is what you want anyway! You should never really run your RAM at higher speeds than that required to 'synchronise' with the front side bus speed of your processor. Doing so can cause performance drops.
Having RAM modules which can operate at higher clockspeeds, however, allows you to overclock by increasing the processor's front side bus peed, and still have your RAM operating 'in sync' with it, and thus at its full efficiency :)
Didn't want to hijack the other thread with this question, so starting a new one here.
Interesting topic that you've brought up here. I don't want to hijack this thread, but just need clarification. If I've got a chip with a 333 FSB, and I'm running 400mhz RAM, what type of performance would I get by lowering the speed of my RAM down to 333? Would it even make any difference?