UPDATE: 9/17/2010

It looks like mIRC has started expiring when it wasn't before, and the thundercity.net website isn't working lately, so here are instructions for using IceChat:

Go download IceChat: IceChat IRC Client :: IRC Client Extra-Ordinaire :: The Chat Cool People Use

When it comes up when you run it, on the left click the Add New button and put in irc.thundercity.net, then choose irc.thundercity.net from the list and click connect. It will connect and you'll do /join #flopturnriver like normal, etc.