When did you buy such a computer?? All computers that are sold these days should be SATA.
A SATA drive should work though an adapter or via usb but I would not think it's worth it. I would be returning the desktop!
Gotta agree here, there should be at least one or two SATA headers on the mobo if it has been made in the past few years. It may currently only be hooked up through IDE but I'm thinking SATA is available somewhere on the mobo - I'd open it and take a peek.