I've had a similar one MTOW, an IRC.backdoor.sdbot anyway . It is pretty nasty, basically allows someone to control your computer through IRC. Generally its used to launch DOS attacks or similar.
It was a while back but I finally nailed it in safe mode by sifting through recently modified files. None of the anti-virus packages I used picked it up. It would launch from system32/dllcache though if you deleted that then it would re-appear a couple of boots later. I'm afraid I can't remember where I found the 'mothership' virus if you like, in all it took me over a month I reckon.