I run an office with three employees. When we had a problem with our time clock reports, I asked one of my employees if she could help me reconstruct her hours worked from memory. Understandably, her answer was, "no." She recommended that I check our domain server to see when her computer was logged in. Is this possible? I need to see all the times that she logged in or out between Dec. 19 and Dec. 31.

you could have a look at the event viewer. This will give times of certain things may help in the determination of when the machine was turned on and off. This is by no means a fully crystal clear way but it may help.

The Event Viewer on the local machine should have the entries in the Security category - however I can't reproduce this on my VM copy of XP.