Thanks for the replies, all. Unfortunately my problem has worsened. First of all, the hard drive was only about 72 Gb, so I don't know why the original XP disk wouldn't recognize the drive upon bootup.
Anyway, I created a slipstreamed install disk with SP2... it still wouldn't recognize any hard drive when booted from it, but when booting into windows, I was able to begin the install process.
Then suddenly the computer rebooted 2 minutes later...so of course now I can't boot into windows (I get a BSOD) so I'm dead in the water now. What can I do next? How can I format the drive somehow so that it'll be recognized by the install disk?