Blocking Googletalk

Google Talk uses Jabber protocol. Jabber is best known as "the Linux of instant messaging" -- an open, secure, ad-free alternative to consumer IM services like AIM, ICQ, MSN, and Yahoo.

Google Talk offers you: Choice(Get in touch over email, IM or a call), Quality(Talk through your computer but hear your friends as if they were in the same room), Convenience(Your Gmail contacts are pre-loaded into Google Talk so inviting or talking to your friends is just a click away).

Google Talk use TCP port 5222. If this port is blocked, it will failed to login.

Because Google Talk use the fixed port, so you can block them only by disable port 5222 in the firewall.