HELP Please: win32.agent.yr

WinXP Pro ver 2002 SP2
Firefox 1.5.0.10
Spybot S&D 1.4 definitions updated 2007-02-28 (latest as of now)
AdAware SE Personal Build 1.06r1 def 2007-03-03
Symantec AntiVirus Corporate Ed. 9.0.1.1000 Scan Engine 71.1.0.11 def 2007-03-02 rev. 52

AdAware and SAV caught nothing. Spybot s&d scan said I have the trojan win32.agent.yr and claimed to have fixed the problem. I scanned my system once more but it was still there (again it told me the problem was fixed). Rebooted in safe mode, Spybot s&d didn't even find the trojan in safe mode (found some tracking cookie called avenue a or something instead). Rebooted normally, scanned again, win32.agent.yr still there; back to square one.

How do I get rid of it?

The only place that appears to offer a solution is here but alas, I don't speak the language of the moon:
http://forum.zebulon.fr/lofiversion/index.php/t116672.html

Thanks!

Boot with ERD Commander or BartPE or something like that and delete the file.