The following is what is recommended by Symantec for similar problems...
The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.
Disable System Restore (Windows Me/XP).
Update the virus definitions.
Run a full system scan and delete all the files detected as (whatever the trojan name is).
Delete the value that was added to the registry.
EDIT: Here is an example...
Symantec Security Response