There's no way of knowing really if it's done any damage, usually AVG will remove and repair any damage done by a virus but the main thing here is you have stopped it causing any more mischief.
If it was a trojan it's probably unlikely to have done any lasting damage to your computer as their main aim in life is to log things like your surfing habits, keystrokes, or in the worst case scenario access your password files & send information back to base.
Have a look here for more information about trojans:
http://www.nohack.net/trojans.htmI wouldn't be overly concerned about it now, but if you are still worried you could change your passwords for anything sensitive that you access from your computer.
It's just another good case for having a firewall. :)
HTH