We use both of these programs with Vista and XP. We highly recommend them.
You can try them at No Cost
Registry Smart  and Repair XP Pro 100% XP & Vista Compatible
(Great programs) The most comprehensive system repair tools on the market.
 

How to change a drive letter in Windows XP
It's not as simple as you might think.
+ Open the control panel.
+ Open Administrative Tools.
+ Open Computer Management.
+ On the left side, open Disk Management.
+ On the right side, you'll see a listing of the drives on your computer.
Click on the drive you want to modify.
+ Now right-click on the same drive.
+ Select Change drive letter and path. Now you can assign a new letter to your drive.
Don't change the letter of the C: drive, because Windows needs to be on the C: drive, and changing the letter can confuse your operating system.

* The hottest Registry cleaning software on the Net today!

* Repair XP Pro - (Great program) The most comprehensive system repair tool on the market.

* Scan your PC for errors absolutely Free (Very good)

* If you use Google AdSense™ Read this page Correct Keywords can pay you more money

* Evidence Eliminator - Erase your surfing history total "privacy protection".

* Double the speed of your PC!Discover the secrets to speed up and optimize your PC in minutes!

* 100's of Very Good Assorted Free computer programs.