Traffic Shaping

I want  to close traffic to this IM programs. I know exist the web option to chat with (both), but I want to close only traffic to the program utilitys: Yahoo Messenger and Windows Live Messenger.
Note: keep Skype.

I hope the new 2010 Monowall features permit do it easy.

I would check the port being used for the IM traffic.  If all else fails capture the traffic with wireshark and then block that port.  However, IM traffic can be sent over port 80 - which means it might be better for everyone to just remove/block the application on the OS level than to block port 80 on the network.

it Needs Layer7 filter
could be done with zeroshell.
regards
Mohammed