
Network is Quakenet.org
Channels #nexuiz (Main) but also #nexuiz.de #nexuiz.se #nexuiz.be
If you've never used an irc client before its very easy install. i recomend xchat because its available for linux/mac/windows
1. download Xchat windows, linux version should be avialable with most distributions, src is here
2. start xchat and you will be prompted with Xchat Server List window.

3. find QuakeNet in the Networks list, check Skip server list on startup option below and ofcourse choose a nickname
4. Click Edit and select a server near you and check autoconnect at start up

5. put #nexuiz in Channels to join field.
6. Click Close
7. Click Connect
Congratulations you're now connected to irc and on #nexuiz main channel. From here any user can help

EDIT2:PLEASE expect to wait longer then 10 min for a reply!
People don't sit and read every line every minute, it's more common to glance at what's been said now and then. So please have patience.
EDIT:here are some alternative clients that GDI+/esteel Posted in another thread (just copy'n'pasted)
Windows:
http://www.hydrairc.com/
http://www.talkative-irc.com/
http://www.icechat.net/
Linux:
http://konversation.kde.org/
http://www.ircreviews.org/clients/platforms-unix-x.html
http://www.emacswiki.org/cgi-bin/wiki/EmacsIRCClient (for übergeeks)
futher reading here http://en.wikipedia.org/wiki/Internet_Relay_Chat