Locking an NT workstation has never been easy. Windows 2000 has a new function, LockWorkStation, that can lock the machine instantly with a single API call:
Private Declare Function LockWorkStation Lib _ "user32.dll" () As LongCall LockWorkStation
In fact, because this function requires no parameters, you can reduce the code to a single line, as well as make it callable from 16-bit code, by invoking it through rundll32:
Call Shell("rundll32 user32.dll,LockWorkStation", _ vbNormalFocus)
The workstation locks instantly when this line is executed. Here