disc brakes are awesome, god's gift to cyclists who want to stop fast. the amount of money/trouble required depends on a few factors.
a)whether or not your fork has mounts. if the left fork blade has a bulge with some holes in it, you're probably good, if not you'll need a different fork.
b)the mounts and spacing on your frame. as MIN will tell you, 130mm spaced disc wheels are few and far between. 135mm spaced disc hubs are much more common. if you have mounts then great, otherwise a disc brake up front with a canti on the rear will provide 90+ percent of the benefit.
what you got?