I'm glad you had success with this. It's scary to think that your firewall and antivirus software can't stop these IRQ_HOOK trojans. But that's the point of them, to fly under the radar and locate themselves hidden in the processes of a program so that they go unnoticed. I'm not sure the intent of the trojan. What was it doing?
I'm really disappointed in the major antivirus software companies, i.e. Norton and McAfee. On the flipside I'm really impressed by the freeware companies who care enough to make their hard work and efforts free to anybody who needs it. Really impressed by these companies.