Mark,
I'm hoping that you have some form of anti-virus protection such as Norton or McAfee. But if you're a cheapskate like me, get AVG from
http://www.grisoft.com. It's free and regularly updated. It will in all likelihood find the offending files that comprise the trojan, and give you their file names. If it cannot remove them for some reason, search for the file names on your hard drive and delete them everywhere they might occur (including your registry). If you're familiar with REGEDIT and are comfortable with deleting or modifying keys, then you're ahead of the game.
Hope this helps.