To do this you need at least one more user account with administrator privileges (f.e. I want to move my user profile named Username to another partition and I will use default Administrator user to do this).
First you need to reboot your machine and log in with theAdministrator account and do the following:
Copy your documents from “C:\Documents and Settings\Username” to another location f.e. “D:\Username”. If you get any warnings asking you if you are sure to move those files answer”Yes”. When Copying is finished, you will no longer have directory”Username” in your “C:\Documents and Settings Folder”.
Start RegEdit by typing “regedit.exe” in your “Start\Run” menu. Find the following key:
"My Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList\" you will see here a set of subkeys starting with S-1-5-21-****
browse trough them and look for value ProfileImagePath that looks something like this : “%SystemDrive\Documents and Settings\Username”, and change this value to “D:\Username”.
Now all you have to do is log off as Administrator and log in with your Username account.