Have you verified in Windows what speed the CPU is actually running at?
I know several BIOSes that will not report the actual speed, but just the one that is closest.
Go get <A HREF="http://www.h-oda.com">WCPUID from H.Oda</A>, and verify what you are actually running at before you pull all of your hair out.
And, If your running a Via Apollo MVP3 chipset board (sorry too lazy to look up yer board), just run the memory at 66MHz and the bus at whatever.