If you haven't made any games yet, then jumping into a multiplayer isometric game is probably a mistake. You'll quickly get overwhelmed and lose your motivation as you hack things together into an unmaintainable jumble of spaghetti code.
Have a look at this article. It tells you which games you should make first and why:
Oh, and I really liked what little time I spent with the
Irrlicht Lidgren networking library. I don't have a ton of networking experience but I got some basic multiplayer logic going without too much headache.