You will need to purchase a rack than can be attached to the seatstays, like this one:
Old Man Mountain Rack - WhiteRock
http://www.arkel-od.com/racks/whiteR...asp?fl=1&site=
Axiom and Blackburn also make similar racks with seatstay compatibility.
You made need some p clips from the hardware store. Try to get them rubber coated.
If not, you can cut strips of rubber from and old inner tube to buffer the p clip and frame.