Ok, it's proven to be harder to set up than I had hoped. So used to two clicks and everything works out of the box. This time I had to click about 4 things and actually type stuff to work.
I basically downloaded Xchat from http://huw.org.uk/smfirc
Once installed, just create a new connection, call it for example SimpleMachines.
Go in there to add a server (irc.villageirc.net).
Specify channel to be #simplemachines
Then you should be able to connect (just like Antes described in his/her earlier post on June 21, 2011).
For some reason after connection, it still asked me to /join #simplemachines
in order to enter that channel. So I manually /join ed and that's it. Just 7 or 8 people in there. Quite an anticlimax.
I vaguely remember Mozilla has an IRC plugin which lets people type something like irc://irc.villageirc.net#simplemachines and that'll let you connect from within Mozilla. Forgot what plugin it was. But that's probably gonna be easier than using XChat.
By the way one of the earlier posters mentioned http://www.simplemachines.org/teamchat/pjirc/
That link no longer exists.
@bonexx5: there are loads of good mods. A good one to start with may be Bad Behaviour which blocks spammers.