I just tracked down a fix online, and it worked like a charm. This guy posted a fix:
Reposting the contents here in case the link disappears:
"Turns out ATA/IDE controllers will often revert back to PIO mode instead of Ultra-DMA. (MS KB article on the problem here.)
Check the problem by examining the controller’s Primary and Secondary IDE settings: Device Manager -> IDE ATA/ATAPI controllers -> Primary or Secondary IDE Channel -> Properties -> Advanced Settings. Look at the Current Transfer Mode field. If it’s “PIO” then it’s a FUBAR PITA and you’ll need to uninstall the driver, reboot and let XP do its magic reinstall. "