I don't think you understood what I was saying. The only developing environment you can use if you want to use xbox avatars is XNA. That is Microsoft's proprietary code libraries to produce a game for xbox indie marketplace. Otherwise you'd have to pay upwards of ten grand for a license to develop for xbla.
if you plan on using xbox avatars then your ide choices are just 1. XNA for visual studio. Unfortunately, XNA doesn't do 3D that well. It can, but it is very difficult to make a quality 3D game for the indie marketplace.
If you're thinking Sims style then you"ll want an isometric viewing angle. Any idea what tool you'll use to make the game? I would suggest unity. It's a great free 3D game making ide that supports all current platforms (xbox, wii, mobile, pc/mac, etc). Unity will also act as publisher if you choose so to help distribute your game.
not really enough information there to gage interest :P Is it a 3D, 2D? Action, puzzler, platform, etc?
