Yahoo messenger - pass firewall

Maybe you can do custom ports with Yahoo!, but I'm sure that Miranda overcomes a firewall that only allows port80. I'm using it with Yahoo! and MSN as well.

if i install proxy at client pc(that have internet access), can firewall detect it?

It would make sense to set a proxy in a host that is not behind the firewall that prohibits you from connecting to some service. It would then be possible to tunell whatever traffic you want, out of the firewall to a port that is not blocked for outgoing data, through the proxy that you will have configured to listen to that port. It would be pointless to to set a proxy in a host that falls under the same firewall rules as your computer.

If all that you are looking to do is chat , try this out
www.e-messenger.net/

Nice link...