OK, all of you who think I'm wrong please have a look into the KT133A datasheet - yes, it's "confidential" but available to everyone from the KT133A product page
http://www.viatech.com/products/prodkt133a.htm ...
http://www.viatech.com/datasheets/DS8363A010.pdf
namely PDF page 33 (document page 27), register 69, "DRAM clock select". No other options than 100/100, 100/133, 133/133.
VIA's 694X/Z chip (for Pentium-III CPU) is more flexible - it can run the RAM on the CPU clock at 66, 100 or 133MHz, or on the AGP clock at 66 regardless of CPU clock, or on CPU+PCI for CPU/RAM combinations 66/100 and 100/133, or on CPU-PCI for 133/100 or 100/66.
To summarize the CPU/RAM clock options, KT133 allows 100/100 and 100/133, KT133A adds 133/133.
694X/Z can do CPU/RAM clock modes 66/66, 66/100, 100/66, 100/100, 100/133, 133/66, 133/100, and 133/133. 66/33 and 133/166 are technically possible but discouraged for obvious reasons

and 66/133 (PC133 SDRAM with a Celeron) is impossible.
Which of those are actually offered is at the choice of whoever writes the board's BIOS.
Regards, Peter