Do they make an adapter ring to put a vivitar 90-230mm lens on a canon xt rebel camera?

It depends on the camera mount on the Vivitar. I know they make adapter rings to fit Olympus OM mount lenses on Canon DSLRs. You might want to check out Steve Gandys' site for other ideas. If this is a manual focus lens you'll have to manually stop down the aperture...

Who is "they"? Perhaps you need to direct your question to Vivitar detailing what lens you are referring to.