I know very little about porting to the XBox360. My guess is, it would not be as easy.

I can't share much information about the XBox development process. I signed many NDAs, and Microsoft does take them seriously. I can say that if I wanted to get a head-start on developing for the XBox without a dev-kit, I would buy a Celeron 733 MHz with 64MB of RAM, a 64 MB GeForce3 video card with TV out, and install Windows2000 and DirectX8 on it.

I would also look into the “Live Arcade” feature of both the XBox and XBox 360. Unless you have a large team (with an even larger amount of funding), you are much more likely to get a game accepted as an “Live Arcade” download than a full retail box.