go here and do an online scan
let that scan in normal windows mode. if it doesnt delete the file, it means its running and cant be deleted.
if you know the trojan file name, just press control+alt+delete and goto process and end process on the selected .exe
if it doesnt show up there
go into safe mode, boot the computer up and before the windows xp screen appears hit f8 key and select safe mode with networking
than run that scan again.