How can I change the physical location of "My Documents" folder?

By default, the My Documents folder for your user account resides in the %Userprofile% folder:
Example: C:\Documents and Settings\Games\My Documents(Assuming your user account name is Games)
If the system drive is running out of space and you want to redirect the My Documents folder to a different partition, follow this method:

1. Create a folder in a different drive
2. Assign appropriate folder permissions
3. Open My Computer window.
4. From Common Tasks pane, right-click My Documents and choose Properties.
5. Type the target folder path and click Apply