Hi, Rick,
I've just spent the last couple of weekends getting my head around XML and FileMaker's export grammar. It looks very daunting at first, so I feel your pain. In fact, it took me over four years to get around this fear (it is a problem that we have had for that long).
I am still very much a novice at XML, but having now got over that hurdle, I must say that it is not as bad as it seems. There is a logic to it. You have to write an XSLT stylesheet and tell FileMaker to apply this stylesheet to the XML it exports. The XML that comes out will be in a row/column format, with the names of the corresponding fields listed towards the top of the XML. You will need to understand the structure of the XML the revenue expects (I find actual examples of expected XML to be more useful than dry documentation), and get the stylesheet to write out the bits of the structure, interspersed with the data from the exported XML file, using <xsl:value-of select="fmp:COL[2]/fmp:DATA" /> etc.
I found the chapter in my "Special Edition: Using FileMaker 9" book (published by Que) to be particularly helpful. There is a detailed walkthrough both of importing and exporting data. I suggest you either get a copy or try to borrow it from a library. The other material I have found useful is "XML in a Nutshell", published by O'Reilly, which I am currently reading.
Hope this helps. Good luck!
Regards,
Chong-Yee