On adding a new drive to the system after Windows XP is installed, the drive letters of the new partition succeed that of the optical drive. If you’re used to having the optical drive’s letter last in the list under ‘My Computer’, you need to interchange thedrive letters. Here’s how you do it:

  • Disable the optical drive before you proceed to interchange the drive letters.
          If the optical drive is active, you won’t be able to interchange the drive letters of
          the new hard disk and the optical drive.
  • Right click on ‘My Computer’ and select ‘Properties’.
  • Under the ‘System properties’ dialog box, click on the ‘Hardware’ tab. Bring up the ‘Device Manager’.
  • Expand the heading ‘DVD/CD-ROM’ drives.
  • Right click on the listed optical drives and disable them.
  • Exit the ‘Device manager’. Now,interchange the drive letters.
  • Right click on “My Computer” and select “Manage” from the context menu to bring up “Computer Management”.
  • Select “Disk management” under the heading “Storage”. All the existing partitions will get listed in the right pane.
  • Right click on the drive letter you wish to change and select the option “Change Drive Letter and Paths”.
  • Click on the “Change” button in the next dialog box and choose the new drive
    letter from the drop down list. Since you disabled the optical drive, you will now
    get the option to assign the drive letter previously assigned to it.
  • Click on “OK” and exit the “Computer Management” application.Now, enable the optical drives you had disabled.
  •  Head back to the “DeviceManager” and enable optical drives. 
Job done! Go to “My Computer” and check the drive listing.