Need help removing a trojan...

My anti-virus software (Trend Micro PC -cillin Internet Security) found a trojan in a file called urqrrqo.dll in C:\WINDOWS\system32. The software won't clean it, and the file refuses to be quarantined or even deleted. The trojan itself hasn't caused any problems yet as far as I can tell, but the antivirus software keeps notifying me of the trojan every 0.5 seconds or so, which is getting really annoying. Any help anyone could provide would be greatly appreciated.