From BlenderWiki

[edit] Installation

The first step to getting involved in IRC (Internet Relay Chat) is finding the right program for you. To keep it simple, for today, the right program for you is X-Chat. If you're on Linux, you probably have X-Chat already on your system, or available in your package repositories. If not, try to find an installer on this page:

http://xchat.org/download/

That page also lists OSX installers that I have not tested, but likely work.

If you're using Windows, go here and download the latest installer:

http://www.silverex.org/download/

[edit] Configuration

Armed with your X-Chat installation, you're probably eager to get connected, right? First, you need to choose your online identity, select which server you want to connect to, and pick your chatrooms (yes, there are many).

1. Open X-Chat, if you haven't already.
2. Under “Nick name,” enter the name that you would like everyone to see. Pick something quickly for now, you can easily change it later. Put something under “Second choice” and “Third choice” as well.
3. Under “Networks”, scroll down and choose “FreeNode.”
4. Press the “Connect” button.

[edit] First connection

You should now be connected to the FreeNode servers; however, you are not yet actually in any chatrooms. You need to join a chatroom, called a “channel.” In the area towards the bottom of X-Chat where you can type, enter the following:

/join #blender

You should now be smack-dab in the middle of wonderful Blender chat heaven. However, being in #blender isn't enough. Many chatters are sitting in six to seven Blender-related channels at any given time. Join a couple more channels to see what I'm talking about:

/join #blenderchat
/join #blenderwiki
/join #blenderqa

There are many other Blender-related channels. Here's a list of some of them:

#blender – Blender-related chat in English
#blenderchat – also Blender-related chat in English
#blenderwiki – discussion about the wiki
#blenderqa - Blender question and answer chatroom  
#blenderadictos3d – Blender chat in Spanish
#blender-fr – Blender chat in French
#blender.de – Blender chat in German
#blenderpraat – Blender chat in Dutch
#blenderchar – Blender character animation discussion
#gameblender – Blender game engine discussion
#blendercoders – place to go if you want to help develop Blender
#blendercompilers – for the brave souls that need help compiling Blender
#blenderpython – Blender Python coding discussion and help