an "extra" drive as you say, you can afford to loose all the data on it...reformat it. Right click on the drive in Windows Explorer. You'll see the option to "format" it. Make sure you select the proper file formats (ie..NTFS, FAT32).
and life goes on...
I bought an external enclosure for an extra hard drive and can't figure out how to get the Win Xp OS off of it.