Actually, I believe that the drive letter should change from system to system, since XP/Windows recognizes a drive based on the drives already connected (unless you have already assigned a specific letter).
Priority goes to C: (boot drive/partition), D: (optical drive, if it is the only other drive attached when installing XP)...and then everything else just rolls up the alphabet when attached.
So a drive which is E: on one system may be picked up as E: on another system when installed (if it is the 3d drive attached on that system).
Another point of confusion for Windows occurs when you have a drive already with a given letter...and you attach another drive with the same letter assigned. In such cases, My Computer will not see one of the drives and the user must go into Disk Management and change one of the drive letters for one of the two drives.
I suspect that simply deleting your USB controller and rebooting...and then attaching the drive.. will straighten matters out on each system.
Edited by hamluis, 08 December 2007 - 01:21 PM.