here a try. I've toke one of the maps posted on the map topic. It was jpg but was the best i found quickly.
Honestly the 256 colors work nice also here, look down.
Map png Normal -- (214 kb)
Map png 256 -- (81 kb)
Bytheway, i hope that the items on the minimap aren't fused with the land Image. Minimap should be faster if all the items (trees, houses etc) are little icons saved inside the client and the server tell to the clients the coordinates where those should be showed. The only graphics server should give you, then, will be the lands and some text.
In any case the 256 colors whould be a nice improvement, if arent already used or if the minimap isn't in an extention that i don't know and all this posts are useless.