Guess I'll reply to my own question - since I have a reasonable answer
and to help those following in my footsteps.
Basically, barely anything at all over at Game Warden that's usable, mostly
screen shots and comments on how it looks - not how it's put together.
So....
Both the HUD and the menu graphics are control by the tbl files, sadly.
The HUD is a system of positioned displays coded in by position using pixels and
directing that particular gauge to a spot. The 2D image used for the display, is also
based on a gauge by gauge basis.
Basically, if you want to make a custom HUD, such as porting from one game to FS2.
You'll have to modify all the gauge's positions, plus other basic tbl changes.
This is closest thing to a guide for the gauges section.
http://www.hard-light.net/wiki/index.php/Hud_gauges.tblDidn't find anything as to the other menu graphics, unless it's a part of the
main hall tbl. Which doesn't appear to be the case.
http://www.hard-light.net/wiki/index.php/Hud_gauges.tblEdit -
Likely, the listings for the menu bitmaps would be a part of this section.
menuui (Handles all the misc user interface, such as the main menu, tech room, campaign list etc)