I bought the 512mb pc2100 when it was 106 at Frys a couple weeks ago, seems to be working fine on my P4 1.7 MSI 645 motherboard combo I bought a few weeks earlier.
I do seem to be learning a hard lesson about reusing an old SMC 9332BDT ethernet adapter (XP calls it generic intel 21140, SMC has no XP driver I can find, and it hangs and drops connections every couple hours).