I can't specifically help you, but I think if you look through the manual or google your webcam model, you should find info on what ports need opening in your firewall.
I'm pretty sure it will use different ports to your Yahoo messenger.
If you have continued problems, post your webcam type and Operating system, service pack, and any third party firewall programs, and someone may be able to provide more assistance.
Good luck sorting it out.
MartyMcFly
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