It's relatively easy as long as your frame has the disc mounts, which you've confirmed it does, the fork also has them, and you have disc ready hubs.
Most forks sold within the last 4 years have mounts, so you should be fine there.
The big thing is the hubs. If they are not disc ready, you'll need to buy some. It usually cheaper to buy a whole new wheelset as opposed to buying new hubs and having them relaced to your existing rims. Check out
www.pricepoint.com for good deals on disc wheelsets.
Also for good deals on disc brakes. I'd spend the little bit extra and buy a set of Avid's instead of the Tektro's your Dad has.
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