This post explains how, by way of a registry hack, you can change the location of the user profiles store from “%systemdrive%\Documents and Settings” to where ever you wish.
1. Create a folder, name of your choice on the D drive you wish to use.
2. Log in as an administrator and copy all profiles (except the one currently being used) by dragging the folders to the new location. After all other profiles are copied to the new location, the profile that is currently being used must be copied as well. To do this, log out of the current account and log in with another account that has administrator privileges. The remaining profile can then be copied using the same procedure
3. Change the default location of new user profiles. Start > Run > “regedit”:
4. There are a series of entries below the Profilelist key that represent each user account currently stored on the machine. For each of these keys, the ProfileImagePath key must be changed to reflect the new location of the profile. It is best to perform this task with as few profiles created on the local workstation as possible to minimize the amount of time required.