as far as wheelset compatibility goes... your bike undoubtedly has a 100mm front axle 'nut to nut' spacing (this is measured at the inside of the fork tip to the other side), nearly all bikes have this same number, except certain VERY heavy duty mountain bikes. Your rear wheel is probably 135mm nut-to-nut (same thing, the space between the rear 'dropouts' that the wheel mounts on), this is the standard mountain bike size. road bikes use narrower sizes, typically 130mm for the latest with 2x10 gearing, and 127mm for earlier 2x8 or 2x9. See http://sheldonbrown.com/frame-spacing.html#spacing for a discussion on this.

I wouldn't bother to try and convert a mostly-road bike to disk brakes. they weigh more, and put more stress on the frame. While they are nice for serious hard core mudders on a full mountain bike, caliber brakes (including v-brakes, cantilever, sidepulls) work just fine, even in the wet. Keep the brake pads and rims clean, keep the pads and brakes well adjusted.