Active Directory does not keep track of which users log into which
workstations. Active Directory does not even know who currently is logged
into which workstation.
I believe there is no way to determine (after the fact) how many times a
user has logged into a workstation. You might be able to tell which users
have logged into a particular computer using WMI to retrieve information on
the profiles saved on the machine.
You could use logon scripts to log the user and computer name to a shared
log file. This would allow you to tell which users logged into any
workstation, and the number of times. I have an example VBScript logon
script linked here:
http://www.rlmueller.net/Logon5.htm