If you can obtain an Xbox debug (green) or dev (crystal) kit, then you should have access to the real XDK CDs and an account on Xbox Central...

If you're talking about buying one of the debug kits that show up on ebay from time to time, be very very wary - assuming its not a fake auction (most are), it's illegal for anyone who has a dev/debug kit to be selling it to somebody who isn't a licensed Xbox developer. At best it's a contract violation, at worst it has been stolen...

The main advantage the debug kit has over the retail kit is more memory*, but as far as I'm aware, OpenXDK is extremely limiting in terms of what you can do with the console anyway, so needing extra memory for most hobbyist development is unlikely.


[*].

there are ways to upgrade a retail machines ram if your not affraid of soldering