Does this mean that DDR ram "clocks down" to whatever the
memory bus speed is, or only that DDR400 will run at
333?



There won't be much of a performance difference at all. If you have to
make a compromise, try a 333FSB processor with 400FSB RAM. The reasoning
is that it is somewhat more likely that you can use DDR400 RAM on your
next upgrade, and you won't pay that much more for DDR400 RAM, which will
run just fine with a 333FSB processor. -Dave