From an account with Administrator level access:

1. Click Start -> Run and type regedit and click OK.

2. In Regedit, highlight the HKEY_USERS key and go to File, Load Hive.

3. Use the File Open dialog to go to the Documents and Settings\<username> folder, where <username> is the account you wish to modify.

4. Highlight the NTUSER.DAT file in this folder (usually a hidden file) and select Open.

5. You'll be prompted to enter a "Key name". You can use whatever you wish, but I use the User's logon name.

6. You can now expand the Hive you just loaded and make any needed changes.

7. When finished, highlight this Hive again and go to File, Unload Hive.

Note: You must unload the Hive prior to logging on to the users account.  Otherwise XP may have trouble loading the user's profile.