Map Utility, How hard would it be? Options

[hunter5150]

I've been brainstorming recently, and I have an idea that I would like some input on.

Many of you are familiar with the DnD Computer game "Neverwinter Nights". One great feature of the game is the map engine that allows a GM to run a game over a network. It makes creature spawn and the like easy. What I want to know is, is anyone aware of a modern tileset that can be used with the neverwinter game or possibly another map utility that would work much the same. I'm looking for the ability to create my own maps, the "fog" that clears as a char proceeds through the map, networkable (preferably with the ability to hide objects from players while having them visible on GM comp), and ability to insert random "ninjas" as I see fit.

If none exists would any tech-head types have any idea how difficult it would be to create this program from the ground up. Scale of 1 - 10, 1 being excel spreadsheet 10 being windows operating system.

Thanks if advance for time and responses.