How do we interactively Debug a script with no user input?

Take the following sample of code:

 ; Check the following key for W2k Machines to make the window not run minimized
 IF @dos = 5.0
 $debug_mode="no" ; - yes/no - no = no user output will be viewed
       IF 1 <> ReadValue($hklms+"\Microsoft\Windows NT\CurrentVersion\Winlogon", "RunLogonScriptSync")
             IF $debug_mode="no"
                   ; -- This will display nothing on the screen (suppressed)
                   $ = WriteValue ($hklms+"\Microsoft\Windows NT\CurrentVersion\Winlogon", "RunLogonScriptSync", "1", "REG_DWORD")
                   ; -- This will display a 0 on the screen for successful Registry Write
                   WriteValue ($hklms+"\Microsoft\Windows NT\CurrentVersion\Winlogon", "RunLogonScriptSync", "1", "REG_DWORD")
                   ; -- Wait a couple of seconds to verify the results
                   SLEEP 2

So, What did we do here?

Added a variable - $debug_mode

If set to no, no visible results returned to the user. If set to Yes, there are visible results returned to the user and a two-second SLEEP (pause) is also added for verification.
Utilize these resources:
UDFs (Full List)
KiXtart FAQ & How to's