your RAM runs internally at 166MHZ -1, they tend to do this, my P3 500 runs at 497MHZ. the FSB is 2x the internal speed
FSB of the RAM should be close to 333MHZ
as for the Athlon XP running at 1.67GHZ, the Athlon XP's are designed to run at these lower frequencies, they still perform as well as its equivalent P4. the Athlon XP's have better pipelining allowing them to complete more instructions per clock cycle.