In Windows 7, I moved the location of a user's My Documents to another drive (D) by right-clicking My Documents, then Properties/Location Tab/Move. The My Documents folder contains the Outlook .pst data file for the user (I guess this is new in W7?). The user does NOT use Exchange, it is a PST file receiveing email via POP3 from a Yahoo business account.
After I changed the location of My Documents, I restarted Outlook and as I expected it could not find the .pst file to load. I pointed Outlook to the right location in the D drive D:\Documents\Outlook Files\xxxx.pst and restarted Outlook. It then found the file and loaded the pst successfuly. However, when I hit send/receive I got an error: Task 'User Account Name - Sending' reported error 0x8004010F : 'Outlook data file cannot be accessed.' There was also the same error for Receiving. I checked and its pointed to the right directory in the D drive.
Dont know if it helps, but I noticed that the first time Outlook started after the .pst move, it created a duplicate My Documents/Outlook Files directory but there was of course nothing in it because it was moved, so I deleted this additional directory.