Youll need:
-A strong frame, usually aluminum. For a fairly light DJ frame, try finding a new Kona frame from wheelworld.com, they sometimes have some.
-A fork with 130mm of travel max, I suggest Marzocchi DJ seris, they have never failed me.
-Brakes, for mechanical try Avid BB7, for hydro try Hayes Nine
-Wheels, for strictly DJ II would try to find a set of Ryhno Lites XL, 36h if you please, XT hubs do me fine, and you will need 20mm front hub for some forks.
-Cranks, Truvativ Hussefelt, are cheap and strong
-Pedals, pretty much any platform pedal will do, make sure they are metal, and studded. Also, too few studs can be slippery, and too may can be worse.
-Tires, Ive used kenda K-Rads for DJ and they grabbed very well, especially hard pack, also the Maxxis Holy Rollers are very similar.
Thats pretty much the main parts, other than drivetrain, everything else like handlebars, stem, saddle, grips, etc. are pretty much users preference.