Hm yeah, maybe try this
"To enable or disable file and printer sharing
You must be logged on to this computer as an administrator to complete this procedure.
Open Windows Firewall. (Start, click Control Panel)
On the Exceptions tab, do one of the following:
To enable file and printer sharing, select the File and Printer Sharing check box.
Advanced users can edit the File and Printer Sharing service, and enable or disable individual ports or adjust scope as needed. "
From Windows Help ---- Maybe SP2 is preventing it from working correctly