Trojans are a bugger, unless you know the trojan you've got, and a specific fix tool you might have trouble getting rid of it

May i recommend, on the trojan front at least

Hijack this Log On that sitre you can both download HJT, and paste your log file in for analysis

Also get Spybot Search and Destroy, and Adaware 2008, both are free and good for diagnosing and killing spyware, including trojans (although, as i said before to truly remove it you may need a dedicated remover

Try Avira, although i personally use Nod 32 ive heard good things about Avira. Get Zone Alarm Personal to protect yourself in the future, and, failing all else, back up important files and reinstall windows