um i would say single speed is a must, new seat would help, i cant really see what the fork is other than marzochii, but i would recommend an argyle or dj3 or something like that or pike, i dont know how your bars ride or not, but maybe get different bars, like deity bar and headset ( im kinda biased on deity sutff, im a huge fan of all there stuff) but other than that, i dont know what else. if you dont want to spend a hole lot, just get single speed, and a higher rise bar. but forks would be good and a nice dj saddle
What you should do is take of the front brake, get rid of that mz comp fork and buy a 2006 or 2007 DJ2 or a 2007 arygle 318 or 409. Converting to single speed would be a very smart idea along with getting a good pair of dirt tires like k-rads or holy rollers that will feel good and help you maintain speed in the dirt.
All in all with around $600-700 you can make that thing a dirt jump ripping machine. (Really the only expensive thing is the fork, if you don't want to spend that much you can always just use the MZ comp and you won't have to spend more than $100 by following the other things I stated.)