I simply bought an external usb drive which means a standard ide or sata drive housed in an external self powered casing. For seeing any old ide or sata work with usb then you would simply buy an external usb cage.
Here when looking in the boot order section of the bios and the hard drive list there on this board using an Award version I could easily set the external 500gb as the default boot device. But the problem still remains that it is intended as an external storage device for the most part.
I couldnt say offhand if someone has tried setting a usb drive as default with an adapter. It sounds like you would likely see better results with the onboard ide or sata controller by way of adapter then going through the usb bus however.