Account logon events

You might want to try using the Filter Events option then select Source:Security and Category: Logon/Logoff. Otherwise I've seen some apps that can import this info then allow you to filter, but event viewer can do an ok job of this too.

The answer depends on what exactly you are looking for. If you just want to get the last login date for users then you might want to use the freeware application DUMPSEC from www.somarsoft.com

If you need more detailed information then you mightwant to enable debug logging on your domain controllers.
http://support.microsoft.com/default.aspx?scid=kb;en-us;109626

This will create the following log file on your domain controllers:
C:\WINNT\Debug\Netlogon.log

I leave debug logging on all of the time and it does not seem to cause any performance problems and is often usefull for tracking down which machine a user is trying to log in from.