Can someone tell me if having a firewall interferes with instant messaging? If so, is there anything I can do to avoid having IM problems, and are there any firewall services known to interfere with instant messaging?

As long as you allow the IM application internet access, there is no problem.
Chances are if you launch an IM application, your firewall will ask for permission, and you can check "always allow."
Regards,
John

Thanks for the info!