Wow. How many resolutions will have VCMI in 2010?
[joking] there is still a lot of work to do 
[/joking]
Best way is to take an existing resolution and do not touch palette (indexed palette should be used but not 24\32-bits). Works for me (on gimp). First 8 colors in H3 graphics are used for transparency and the last 32 - for player colors.
Most of details on AdvMap.pcx are actually not used: hero\town lists, resource bar, buttons (except empty ones). All of them are placed in game separately. In your config you have:
HeroList: size=16 …
should be 15 - arrow and 1 item are below infobox. Same with TownList
Just found this thread.
Look at the pic posted by Tow - this is how working palette looks like.
