I will not publish, just test for personal use. So I just want to develop.
You either need to use the Microsoft XNA developer’s tools, or you need to buy the XBox 360 developer kit and the XBox 360 Unity license, both will cost more than you probably have.
So, there is not much you can do unless you are willing to shell out some fairly serious cash.
If you are a student you can get the XNA developers kit for free. The only thing you will not be able to do is publish anything you make without going through a XNA Developer.