If you look in categoryFeed.brs, you'll see that the code is actually pointing to a feed on the roku website:
http://rokudev.roku.com/rokudev/example ... gories.xmlIf you download the xml files that the sample code points to, you can follow along with the code. You could modify those xml files, post them on your server, and modify the brightscript parsers in the sample code to match. As you go through this exercise, you'll find that the categories.xml points to other xml files that you can recursively download and match to the parsing code in the example.
Along the way you'll have to pick up at least "conversational" level BrightScript... it is very similar to VB or JavaScript, so it shouldn't be too big of a stretch if you have any kind of programming background.
--Kevin