Windows XP and 2000 use MountMgr to manage drive letters. The weird thing about 2K/XP is that, unlike Windows 98 or ME where hard drives are assigned letters first, Windows XP and 2000 assign the next available drive letter to each device added, regardless of type. For instance, when I two CD-ROMs added before newest Hard Drive , the CD-ROMs had letters D: and E: while the new drive letters started at F:.

The good news is that drive letters can be manually changed using Disk Management under the Administrative Tools, with some exceptions. For details, here's a Microsoft Knowledgebase entry for this problem:

How to Assign a Drive Letter

To assign a drive letter to a drive, partition, or volume:

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 is displayed 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 in the left pane, click Disk Management.
4. Right-click the drive, partition, logical drive, or volume for which you want to assign a drive letter, and then click Change Drive Letter and Paths.
5. Click Add.
6. Click Assign the following drive letter (if it is not already selected), either accept the default drive letter or click the drive letter that you want to use, and then click OK.

The drive letter is assigned to the drive, partition, or volume that you specified, and is displayed in the appropriate drive, partition, or volume in the Disk Management tool.

How to Change a Drive Letter

To change an existing drive letter on a drive, partition, or volume:

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.
3. Click Administrative Tools, double-click Computer Management, and then in the left pane, click Disk Management.
4. Right-click the drive, partition, logical drive, or volume for which you want to assign a drive letter, and then click Change Drive Letter and Paths.
5. Click Change.
6. Click Assign the following drive letter (if it is not already selected), click the drive letter that you want to use, and then click OK.
7. Click Yes when you are prompted to confirm the drive letter change.

The drive letter of the drive, partition, or volume that you specified is changed, and the new drive letter is displayed in the appropriate drive, partition, or volume in the Disk Management tool.

How to Remove a Drive Letter

To remove an existing drive letter on a drive, partition, or volume:

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.
3. Click Administrative Tools, double-click Computer Management, and then in the left pane, click Disk Management.
4. Right-click the drive, partition, logical drive, or volume for which you want to assign a drive letter, and then click Change Drive Letter and Paths.
5. Click Remove.
6. Click Yes when you are prompted to confirm the removal.

The drive letter is removed from the drive, partition, or volume that you specified.

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Troubleshooting

• When you attempt to change an existing drive letter, you receive the following error message:
  
  The volume volume_label drive_letter is currently in use.
  If you continue, the new drive letter will be assigned; but you can still use the old drive letter to access the volume until you restart your computer. The old drive letter will not be available for assignment until you restart.
  
  Warning: Changing the drive letter of a volume might cause programs to no longer run.
  This error message can occur if there are files in use on the drive, partition, or volume. This includes files that are accessed by other people on the network. To resolve this behavior, use one of the following methods:
  
  
  • Click No when you receive the error message. Quit all programs that are using the files on the volume, and then change the drive letter (right-click the volume, click Change Drive Letter and Paths, and then click Change).
  • Click Yes to proceed with the drive letter change.
• When you attempt to remove an existing drive letter, you receive the following error message:
  
  The volume volume_label drive_letter is currently in use.
  If you continue, the drive letter will be freed; however, it will still be available for use until you restart your computer.
  
  Warning: Changing the drive letter of a volume might cause programs to no longer run.
  This error message can occur if there are files in use on the drive, partition, or volume. This includes files that are accessed by other people on the network. To resolve this behavior, use one of the following methods:
  
  
  • Click No when you receive the error message. Quit all programs that are using the files on the volume, and then remove the drive letter (right-click the volume, click Change Drive Letter and Paths, and then click Remove).
  • Click Yes to remove the drive letter the next time you start your computer.

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