If you have your mind set on disc brakes, you can purchase disc brake adapters to bolt on your frame. Do a search on E bay under disc brake adapters. If it were me, however, I wouldn't get that fancy and put disc brakes on an inexpensive Nashbar touring frame. Many tourers specifically prefer cantilevers for ease of maintenance and repair on the road, and cantilever style works very well when adjusted properly with good pads. Kool Stop makes excellent pads that will fit them.
Last edited by Skewer; 06-20-08 at 09:47 AM.