[Malsua]

Well, I checked that out, and my 512 is a PC100/133, and the 64s are PC133s, so I think I’m OK on that front, anyhow.

Probably, but they may have different CAS Latency values which is why until you get a stable upgraded system, I'd yank 'em out. 512mb is plenty for XP specially if it's just during the installation.

[Tolerance Sucks Rocks]

I’m not throwing them out at this time. I have a total of 640.0 mb and the system seems to run fine at this point. When I do throw them out, I’ll just get another 512 PC100/133 to match.