I don't know if you'll find anyone here that could lend alot of help unless they've had experience with the Dell's. My best guess would be to contact Dell and explain to them that the case is "damaged" and that you need to remove it to put into another case. If you make it sound like you think their case is crap, they may not help you with it.
They should be able to provide guidance. If not right away, then they will forward it to one of their "specialist" (i.e., the only guy in the shop who knows what the term "
mobo" means) and they will get back to you.
Hope this helps.
Rob
