External HDD visible in Win7 but not XP

My 1TB Seagate FreeAgent Go was functioning properly in Windows XP until a few days ago, when I finally installed Windows 7. Both OSes are on my PC, in a dual-boot configuration, and both are clean installs. But now only Windows 7 can see the external HDD; Windows XP cannot.

Actually, the drive is visible in Windows XP's "Disk Management" feature, just not in Explorer. And on one occasion I was able to make the drive show up in Explorer by scanning for new devices in Device Manager, but when I tried to open it, I got an error message to the effect that the drive is "corrupted and unreadable." Yet it reads fine in Windows 7.

I'm only guessing here, but I'm wondering if the System Volume Information folder was changed by Windows 7 in some way that Windows XP can't handle. But whatever the cause, I'm at a loss for what to do to make the HDD work in XP again. I know I can backup the data and then trying a reformat, but that'd take a lot more time (and disk space) than I have.

Can anyone suggest what else I might try?