Read you post then look at the new xbox, then look at the old xbox then look at your post again then look in the mirror and laugh... Only joking. The old mobos won't fit in the new xbox 360 housing without extensive case modifications and where would the hdd go or the DVD drive?
If Youve that expericened then you would no, That it would never fit unless You cut it all up =]
Also where would the fans go? there to big for the slim, the dvd drive? The Hardrive?