Changing Drive Letter Allocation
The easiest solution in order to avoid problems with letter allocation, is to make your main hard-drive and your slave or secondary-drive (if you have one installed) Y and Z; this of course ensures that there are no allocation problems, unless you have a large number of drives installed, which isn’t likely.
The following applies to the Windows Vista operating system; the changes for XP are the same and you can follow the link below for help.
Click on the “Start" menu and go to “Control Panel". Click on “Administrative Tools" (if you have classic view switched on, click on “System and Maintenance" first). Click on “Computer Management:" in the open window look on the left and find the heading “Storage." Click on “Disk Management" under “Storage."
Now you can change or re-allocate a drive letter. Right-click on whichever drive you want to change (i.e. C: or your primary partition for example); a drop-down menu will appear and you can choose “Change Drive Letter and Paths…" Click on Change and re-assign a letter by “Assign the following letter" and choosing on the right-hand side.
Here is an article for changes in Windows XP:
Microsoft KnowledgeBase: Changing Drive Letter Allocation (XP)
Remember that frequently re-allocating hard-drive letter can cause problems. In case of such problems you can run the "Disk Management Utility" or read the following article which deals with some of the problems which you can encounter:
Drive Letter Problems in Vista
Finally here are a couple of related BrightHub articles:
Windows XP won't Boot: Changing Drive Letter for a Partition
Drive letter Allocation for a Reformatted External Hard Drive