1) You said the CPU was 667MHz; does that mean it's a Pentium-3? (Not that this is likely to make any difference - but it's nice to be sure).
2) Have you tried checking the support info at Micron's site?
3) What is the model name of your machine? (For example, the machine on which I am composing this response is a Dell Inspiron 2650 laptop).
FWIW, my guess at this point is that the motherboard (btw, what is its model identifier?) chipset or the BIOS (and which company made the BIOS?) is failing to handle XP correctly. I had the identical problem with an orphaned PC (350MHz Pentium-2 with 384MB memory) when I tried to make it useful again by installing WindowsXP Home edition on it. Eventually, I gave up and returned the PC to the trash where I had found it.
Oh, yes....which variety of XP are you trying to install? And have you thought of adding a hard drive and installing Linux on that? You could then use Linux - I recommend SUSE, but almost any major distro would be good - to back up the data on your C: drive before doing the wipe-and-install recommended by other FReepers. Of course, if my guess is correct (and I hope it isn't), none of what any of us are suggesting is going to do you any good: There may be a BIOS upgrade that you could apply (but there probably isn't), but you may well wind up getting a new PC, anyway.
The computer is a Micron Electronics Millennia with a Pentium III. I am installing the Windows XP Home Edition Upgrade with SP 2. I haven’t checked out Micron’s support yet.