check out the solution here:
http://www.slipstick.com/config/moveimap.aspSteps to Move the PST
Move the IMAP personal folder (*.pst)
First, close Outlook then make sure Outlook is not listed in Task Manager, Processes tab a few minutes after you close it.
Open the profile (Control panel, Mail) and click on Data files.
Select the IMAP acct and click Open Folder to open the folder containing the PST.
Move the PST to the desired location. Do not rename the file Outlook creates a new file in the default location if you try to rename it - you can only move it.
Switch to the Data Files window and double click on the account's data file.
Now you'll get the 'can't find' error and can tell outlook where to find it.
Close the dialogs and you are ready to restart outlook.