The framework and tools team has been hauling A over the last few months to get this to you and they are justly proud of themselves. A key factor in the beta is that you can't deploy to your Xbox in this version - this is mostly to try out things while developing on your PC.
Get setup here if you are new to it all:
If you have the previous CTP or run into problems, our amazing setup pm Aaron Stebner's blog is particularly helpful:
Get help from folks in the forums here:
In a move that entirely trumps When Cods Collide in 2.0, we have Goat Attack by John Kennedy on the new 3.0 stuff:
Live it vivid!