here is a guide:
http://forums.xbox-scene.com/index.php?showtopic=194937
If you have an action repaly, then you can use that instead of the modded box way displayed in that tutorial. Just skip that step Also, linux (is in the gamesave) is needed for that one, but it is also the safest way. It requres a PC to hook up to your xbox.
I have not tried flashing with evox (non-linux way), but as soon as I get a memcard, I can tell you. Unfortunately, it won't be for a while.