Help with File Sharing

I’m having problems in creating a rule to share files with another 2 computers. We connect to internet through a wireless router. All computers have a wireless pci adapter. The problem is the following: I can’t see the other computers until I switch off the LAN monitor.
Can you help me to create a rule to solve this problem?.
Thank you!.

you should define a trusted network and then apply it in forming new rules
allow tcp/udp in from TRUSTED ports 139,445
allow tcp/udp out to TRUSTED ports 139,445

Other issues may apply depending upon your OS (eg OS X, Win/*, Linux)