Download the latest versions (5.7 for Windows 2000/XP/Server 2003; WSH version 5.6, the latest version for older Windows versions, is no longer available):
Darwin Sanoy's IsLaptop script detects if a computer is a laptop "by checking five different WMI classes for data that may help identify the computer as a laptop"
Clarence Washington's site may no longer be available, but much of the code published on his site is now included in myITforum's Code Repository