If you're a telnet ninja and know the IRC protocol, you can use IRC with telnet =D.

I wrote a weak IRC client that's basicly just a telnet clien that handles the pinging and ponging.

If you're looking for a change form mirc, you should try xircon(xircon.com). It's no longer in development, but if you know TCL, you can do just about anything with it, even write what's essentialy a whole new client(kano.net, good script, may not exsist anymore though).