I've been using meebo as my main chat client now for the past couple of months after deciding to use Firefox as my main OS. They apparently now have a way for you to use their site from locations where their site is restricted by installing a repeater client on a machine that has free access to the Internet. So, you would install it on your home computer and then connect your work computer to your home computer to do your chats.

Neat, although this just seems like a whack-a-mole game where your IT admins just keep blocking sites from you (in this case perhaps all the IP addresses of the subnet your home computer connect to through your ISP) until they remove all your Internet privileges and you're restricted to chatting by sending greeting cards and writing your blog posts on an IBM Selectric.