Actually, Mart's example will show that the value located at the Key path is empty. A small distinction, but important to understand as a new scripter. If you need to know if it didn't exist instead of being empty, you could read the location into a variable, then check @ERROR. If the ERRROR macro contained the value "2", then it did not exist.
 Code:
Break on

$key = "HKCU\Software\Work\Config"

$RC = ReadValue($key, "IncludeSubjectLabel")
If @ERROR = 2
	$rc = WriteValue($key, "IncludeSubjectLabel", "0", "REG_DWORD")
	$rc = WriteValue($key, "IncludeSubjectLabelOnBrowse", "0", "REG_DWORD")
EndIf
Also - Registry objects consist of a Key and Value. Values contain Data of a specific Type - this info is needed to Write the object. You can think of the KEY as the PATH and VALUE like the FILE in a disk structure. Functions that deal with keys won't include the value part, which was the issue in your first attempt.

If it's simply important that the registry object contain specific data, then it doesn't matter what method you use.

Glenn
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Actually I am a Rocket Scientist! \:D