Can anyone point me to any good explanations of the templates that FO3's menu xmls use?

Thanks.

This might not be exactly what you're looking for, but I put together a modder's resource that adds a couple of counters to the HUD - one for beer, and one for caps. The code is commented, and it includes some explanation as to how to modify it for your needs. It only covers putting text up on the screen though, no image templates or anything else. I've also updated my technique a bit since uploading it, so if you want something more robust, take a look at the xml files for IMCN or Powered Power Armor. The PPA xml includes images.

http://www.fallout3nexus.com/downloads/file.php?id=12977

Looking through DarN's xml is also a good idea, though there's a lot of that. My resource narrows it down significantly.