SIEGE's IRC channel is located on the Freenode network, in #siege. There are multiple ways to connect to the channel:

With your own IRC client

Connect to irc://irc.freenode.net/#siege (* NOTE below)

With PJIRC, a java IRC client

The client is located on this website: http://irc.libsiege.org/pjirc

With Freenode's AJAX-based client

You can find it here: http://webchat.freenode.net/?channels=#siege

* NOTE: The Mibbit IRC client is blocked by Freenode due to a large amount of spammers using Mibbit as a proxy.