Simply unblock port 54925 for scanning and port 54926 for faxing. Also make sure you allow both TCP and UDP packets.

By default after installing the MFC-440CN drivers the scanner/fax is blocked by windows firewall so you need to unblock the network ports the scanner/fax tries to connect to.

Brother has some nice instructions located here that show exactly how to unblock the required ports.

I ran into this problem with both Windows XP and Windows Vista, but to get my scanner to work I just turned windows firewall off, not really the best practice!