WinXP isn't that old.
The drive format should be either some version of FAT, probably fat32 - or NTFS.
Either would be recognized, and readable, from a Mac, assuming that external hardware is working properly.
Fat32 should be fully usable on any Mac. NTFS would be read-only, unless you have NTFS drivers installed.
If you have the drive plugged in, so it is a visible device in the System Information window, can you see the drive in Disk Utility? If it is not mounted, you should be able to choose Mount, either an icon in the top bar of that Disk Utility window, or choose Mount from the File menu, still in Disk Utility.
If, instead you get the choice to "UNmount", then that drive is already mounted, and you should be able to access it from the sidebar in any finder window. That should allow you to browse through the files on that drive.
You can also, in Disk Utility, choose that external drive, and click First Aid (or Repair Disk on older versions of Disk Utility)
Fat32 should show a repair action of some kind. NTFS cannot be repaired on your Mac, unless you have an NTFS driver installed.