First, check to make sure Dreamhost allows you to setup IRC services on your server. Many webhosts specifically prohibit IRC.
Second, I'm going to assume that you have root access, and it's a dedicated server, right? If not, it's probably a moot point -- you won't be able to install or setup IRC service on it.
Finally, does it have to be IRC, or do you just need web based group chat? If the latter, there are several alternatives that are much easier to setup, and won't require special permission from your webhost. I would look at setting up a Meebo Room (
http://www.meebo.com/rooms/). They can be embedded on any site, and the same "room" can be accessed from any number of sites (if that serves your purpose).