I am fairly certain this has not been done on a 360. I tried Google and got a bunch of "replace and repair of the DVD" but no swaps. Since I doubt you could find a HD that would fool or trick the 360 into thinking it was the DVD tray. I am just in the mood to experiment, back in December I replaced my BenQ DVD successfully and swapped out the PCB. Now it looks like I have to take it apart for some maintenance.
>>>RANT Warning<<<
It better be just a dusty laser.

If it is more than that, I plan to fix it up and just resell the damn thing. I blame the Xbox customers (of which I am one) for buying into this piece of crap. It has the shelf life of a goldfish. If the makers of Xbox 360 ever get into producing cars, I wouldn't be in line to buy one.
<<<End of RANT>>>
Remember when replying, I am talking about 2 HDs on the 360, one in place of the DVD tray. I also realize that such a mod could get you banned.