you probably won't be able to put a new mobo in that same computer case, as most oem manufactures are weird about stuff like that and make their parts so they don't conform to standards. as far as mobo size goes, ATX is ATX, anything atx will fit in an atx case.
you probably don't want that mobo though, I have had nothing but problems with SiS chipsets
the USB ports are 2 on back probably and then headers for more on the board that will attach to the front of your case or something.
anyways, I don't think you need to worry about stuff fitting, IF your case is an ATX, it will all have it's place.