Check out Spector Pro. It does periodic screenshots to track GUI activity. You could probably even use something like Camtasia for screen recording but that may be too awkward.
Before you do any sort of employee monitoring, make sure your employees (admins included) are aware that it may be taking place and have signed off on the company policy stating that. Otherwise, this could come back and bite you.
You can also look at Sonar by Awareness Technologies.