I don't have 2K in front of me but in XP which I would think is the same, if you expand the tree for "Event Viewer" you should see three logs titled Applications, Security and System. The log for "Security" will give you the Logon/Logoff dates and times.
If you still don't see it, be sure you have Admin rights and if not, log in as Administrator and then check the Event Viewer.
If you still don't see it, be sure you have Admin rights and if not, log in as Administrator and then check the Event Viewer.