The stumbling block could be product-tying laws that have plagued Microsoft recently. From the article:
"If you sell software that can run on hardware that you do make and hardware that you don't make, you cannot require people to buy your hardware to run your software," Brookwood says. If Dell really wanted to sell Mac OS X hardware, it could force the issue through the legal system, he says.
It would be ironic if Apple were forced to ship OSX for PCs by court order.