There are several ways:
* You can use ugly yet functional QuakeNet Webchat interface http://webchat.quakenet.org/
* Use dedicated IRC client, I suggest http://xchat.org/ it's open source, free, and looks very ok
* You can also can use classic mIRC http://www.mirc.com/
If you use Pidgin IM client, there's support there. If not, applications mentioned above will be better suited.