You can move the entire C:\Users folder to a different drive pretty easily after windows is installed:

1. Boot to the installation media, and get to the command prompt (I believe you need to click repair first)

2. Use Robocopy to copy C:\Users to D:\Users: robocopy c:\Users d:\Users /mir /xj /copyall

...:. a. /mir tells robocopy to mirror the directories, this will copy all files and permissions

...:. b. /xj is very important, this tells robocopy not to follow junction points. If you forget this, you will have a lot of trouble.

...:. c. /copyall will copy all the attributes includings ACL and Owner info

3. Verify that the files successfully copied

4. Delete c:\Users

5. Create junction that points to d:\Users: mklink c:\Users d:\Users /j

That's it. I've been using this process since Vista went RTM with no problems.