Net Send firewall Port for XP2

I have windows xp service pack 2 and we ahve another machine with windows xp service pack2 or 2000 pack 4. i have sp2 firewall enabled on the system. when i send
message from 2000 machine to XP machine it does not work. when i diable
firewall then the windows message from net send command works fine. The
messanger service and alerter service both are enabled "Automatic".

Can anyone tell me which ports i need to open so that users can send me
messages from net send command and i which port i need to open so that i can
maintain the security instead of diabling the firewall.


This is urgent.
Thanks