So, first of all, make sure you have an up-to-date antivirus program. I suspect that you are using Symantec's Norton Anti-Virus, as you refer to the malware as "IRC Trojan". Symantec provides complete instructions on how to eliminate this malware on their site.
There are a number of variants of this Trojan horse, and I've provided the link to one of them. You may need to search on that site for more info if you have a different variant. Your up-to-date scanner will tell you which one you have.
For more information on this topic, visit these other SearchSecurity.com resources:
David Strom's Security Tool Shed: NAV 2003 is powerful, versatile and easy to use
Virus Prevention Tip: Cleaning out a virus infection
Virus Prevention Tip: Scan and clean viruses via the Web
Virus Prevention Tip: Backdoor Trojan making the rounds
This was first published in December 2002