All partition/drive letters (other than C:) can be easily changed in XP by using the Disk Management function.
The only caveat is that you cannot change a partition letter to a letter which is already assigned to a partition...until you change the letter assigned to that partition.
Example: I have a hard drive with 3 partitions (C:, E: F:), one of which is the boot/system partition containing Windows. The Windows partition letter cannot be changed, but the other two partitions can be changed. My D: is assigned to my DVD burner.
If I want to change the E: drive to D:, I can do so...after I assign a different letter to my burner (let's say I make it Y:.
My drives reflected will then be...C:, E:, F:, and Y:.
I can change either E:, F:, or Y: to D, G, H, I, etc.
All partition/drive letters can be changed at any time, as long as I understand this. I change mine all the time, according to whatever I think makes sense at the time
Disk Management - http://www.theeldergeek.com/disk_management.htm
You didn't ask but...volume names can be changed anytime, using the Explorer right-click.