First question: are your wheels disk compatible? Second question: do your bike and fork have disk brake bosses?
If the answer to both questions is: yes, you can put disk brakes on your bike.
The next question is: do you want mechanical or hydraulic disk brakes?
In my humble opinion, mechanical disk brakes have no advantages over rim brakes unless you are constantly riding in wet, muddy conditions. Otherwise, they are heavier and while they may provide stronger braking action, rim brakes do a perfectly adequate job, weigh less and cost nothing extra.
Hydraulic brakes, on the other hand, require only a feather touch to stop. Thus the advantage is you can take super long rides with epic downhill runs and your hands and arms will never cramp up and/or fatigue from constant braking. Hydraulics, of course, are more expensive. Plus, hydraulic systems include levers so you have to take your old levers off and reroute the cables.
Installing disk brakes can be done by yourself. However, some systems (especially Magura) require exceedingly fine tolerances or the brake pads will drag the rotors. Personally, I'd take the bike to your local bike shop and have them do the job. They'll have the tools to face and/or shim the disk brake mounts for perfect operation. Also, some forks (like Manitou) require an adaptor or disk brake specially made for the orientation of the disk brake mount.
Hope this helps.