The IRC Channel (chat room) that we'll be able to use for this can be found here: http://rbwhitaker.wikidot.com/competition-chat
If you want to connect with a different IRC client (and trust me, there are hundreds of them, many of which have better features than the one at the end of the link above) you can connect directly to it.
You do not need to register/reserve a user name. You can use a different one every time, or use the same one and hope that nobody else comes along and takes it.
However, if you want to get a user name that is reserved for you, you can do that as well. The process is a little different than what you might be used to if you've never used IRC before. It basically involves talking to a service called NickServ directly in the chat room, but you'll be sending private messages to it, so we won't see it. Here's a link to some instructions: http://freenode.net/faq.shtml#nicksetup
I'm not an IRC pro, but if you have questions about it, let me know and I'll help where I can.