Topic: Customize XML Data Source

I have read the help text on the simple viewer site:
http://www.airtightinteractive.com/simp … omize.html
And i need the function To Customize XML Data Source! But i do not understand where to put the variable! I have made the folder to a php string $myfolder and the xml file is the same : gallery.xml

Sorry for my bad english, hope you understands and know how to help me!