If, as you say, the transform is successful then into what object did you transform into. If your results are not xml then you will have to do one of two things, either use the transformNode object to return a string which you can write to a text file using the "Scripting.FileSystemObject" which can then be saved or using a different class for the second argument to the transformNodeToObject. You will need one that implements IStream and the easiest to use in a COM scenario is "Adodb.Stream", available with Adodb versions 2.5 and above.
Once you have created an instance of the stream and output to it then you can save the results to a file. For details of all its methods and examples consult MSDN online.