Check your startup tab in msconfig;
See if anything referring to the trojan is listed, if not, go throught the list and write down anything you don't recognise. Go online to google and search for those items one at a time, in most case they will be ok, it throw up what is causing this trojan to be reinstalled on startup.
It may be a good idea to take a look at the services tab as well.
Hope this helps.