You can see a screen shot of the editor (which uses COM / .NET interop) and more musings about being a toolsmith versus being a game developer over at http://www.enchantedage.com/cargame.

Suffice to say: I may yet move beyond the tech demo stage of one of my hacks, and make a real game of my own one day.

Yes, one day!

Oh, and by the way: GTA IV on the Xbox is pretty good. I'd say 8.5 out of 10. It loses 0.5 because the controls seem to kill me once each mission. It loses 0.5 because of glitchy graphics -- especially a telephone I was supposed to read the number on, and the texture was too blurry! It loses 0.5 on general principle.