Confused about pc3200 vs. 266

If you have a mobo that supports PC3200 (eg a kt400 chip), and you only have a cpu that supports 133mhz fsb (eg palamino 1800+), will you see any performance gain over a setup that only uses PC2100 ram? If so, how much of a gain?

It depends on two factors. First is the fsb. Second is the cpu/mem ratio. For example if you run at default 133 fsb and syn mode, your ram is running at 133x2=266, in this case pc3200 don't have much advantage over pc2100, maybe you can set timing more aggressively with pc3200. But if you want to overclock @ 200fsb, I don't think average pc2100 can run at that speed, your pc3200 is designed to performance there.