I thought this would be easy, and it was - once I figured out one little thing. You'll probably come across Microsoft's KB Article 236621 which got me most of the way there. The second method listed says to search the registry and replace all instances of "Documents and Settings". This works fine if you're just moving the folder to somewhere else on the same drive with a different name. However I wanted to move all the user profiles from the C drive to the same folder name on the D drive on a terminal server.
First of all, trying to do this with the regular old regedit program is awful since it doesn't do search and replace. I found a free program called Blade's Registry Replacer that worked great for doing search and replace on the registry and generating an undo file.
Now that you've got that you'll want to replace all instances of "C:\Documents and Settings" AND all instances of "%SystemDrive%\Documents and Settings" (this is the part I was missing earlier) with "D:\Documents and Settings" or whatever you want to call the folder on the D drive.
