You know the problem, you walk up to a PC and plug in the USB key and it does the little dance ( a few pop up ballons and stuff) and then tells you “Your Drive is ready for use”. You open My Computer and it’s not there.
The computer lied. Well yes and no
You see there is probably a mapped drive letter sitting on top of your key and it won.
Here is the Microsoft Technote
How to change drive letter assignments in Windows XP
How to assign a drive letter
To assign a drive letter to a drive, a partition, or a volume, follow these steps:
1. Log on as Administrator or as a member of the Administrators group.
2. Click Start, click Control Panel, and then click Performance and Maintenance.
Note If you do not see Performance and Maintenance, go to step 3. Performance and Maintenance appears in Control Panel only if you use Category view. If you use Classic view, Performance and Maintenance does not appear.
3. Click Administrative Tools, double-click Computer Management, and then click Disk Management in the left pane.
4. Right-click the drive, the partition, the logical drive, or the volume that you want to assign a drive letter to, and then click Change Drive Letter and Paths.
5. Click Add.
6. Click Assign the following drive letter if it is not already selected, and then either accept the default drive letter or click the drive letter that you want to use.
7. Click OK.
The drive letter is assigned to the drive, to the partition, or to the volume that you specified, and then that drive letter appears in the appropriate drive, partition, or volume in the Disk Management tool.
Here is a slightly quicker version
RIGHT CLICK on My Computer , click on MANAGE
Click on Disk Management in the left pane.
Follow the above instructions from 4 onwards.
If you aren’t sure about which letter to change it to Use Y or W if they are available.
Be careful you are playing with live ammunition.