To limit/restrict what computers a user is allows to login on a Active Directory domain, you first need to open Active Directory Users and Computers.
Next, find the user that you want to limit/restrict and open the Users Properties. Click on the Account tab and then click the "Log On To..." button.
A "Logon Workstations" window will appear. Under "This user can log on to:", select the option "The following computers". Type in the computer name and then click on "Add". Click OK twice and you should be all set.