Transplanting a Mac mini, in to a ATX case would be just so ridiculous. I would buy a Mac mini for its looks and compact size. If I was desperate to add extra hard drive, why would I spent whole lot of money and time screwing and transplanting the creative mac mini on an ATX box? shheeesh.......I'd just buy an external hard drive, as the prices for external hard drives have dropped so much.
Don't forget that Mac mini's have usb ports!!!