It's been my experience that PC100 and PC133 RAM do not work together in a 2 slot configuration. At all. And I can't remember hearing them working in tandem properly at all. At least in the boards I've tried them in (Asus P2B, P2 and a Via motherboard). The P2 mobo held a PII 300, the P2B held a PII 400, and the Via motherboard (can't remember model) ran a K6-2 350.
I suppose it could just be these motherboards, but as I said ealier, I've never heard of them running side by side. Anyone have any solid proof?
And yes, the PC133 RAM will work just fine in a 100MHz bus. The RAM will just run at 100MHz.
Hey, if your motherboard has 4 slots (assuming you're only using 2 DIMMs), try arranging the PC133 and PC100 so there's a free slot between them. That might work.
Also, you can't successfully mix unbuffered and buffered RAM. Sames goes for ECC and non-ECC.
Thanks,
Odonadon