I use AVG Free now. As far as I can tell it just sits there and does nothing. It doesn't do a scan inless I ask it to. It doesn't download updates intill I tell it to. In all it's perfect and well behaved.
Whats more with it runnng my computer doesn't take the best part of a week to shut down.
AVG Free can be set to scan on a daily schedule and the update manager can be enabled through the Windows Task Manager.