Calling a DLL from $SUPPORTDIR$ and Return Value

[Superfreak3]

Currently, I added a custom .dll to Support Files and want to call it from the Next button of our serialization dialog. Here is the logic since I don't know how to actually call something from the dialog control mentioned or if I just script....
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label: Serialize
if variable WIZARD Equals Back
GoTo Label: Readme Information
else
if variable WIZARD Equals CANCEL
GoTo label: Main Install
end
end

Set Variable APP_VALID to 0
Call DLL Function $SUPPORTDIR$\\Our.dll->_OurFunction (get result into variable APP_VALID)
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Now since I'm conditioning another dialog to appear if serial numbers are entered incorrectly or are invalid, which Return Type should I use on the Call DLL Function to receive a 1 or a 0.

Then, after receiving the 1 or 0, I need to call a dialog indicating the serial number entry was invalid (if 0 returned). Would I just append or insert this after the code snippet above...

if APP_VALID Equals 0
GoTo label: Bad Entry
end

Then Bad Entry might be....

label: Bad Entry
if variable WIZARD Equals Retry (there will be a retry button to return to the serial entry dialog)
GoTo Label: Serialize
end

Any HELP is GREATLY Appreciated