Peter just bought a MacMini and would like to run a dual boot OS setup with both OS X and Windows. Leo says he can do that with Boot Camp. To use Windows 8, he'll have to have updated drivers and there are many articles on the web on how to do it. Can he install Windows via USB key? Leo says yes, he can also just download the ISO to his USB key and point to it, and the Mac Mini will install it.
Note, if you're using a fusion drive with the iMac, you'll need to do a hack to get it working. This article explains how.