insteaad of everyone suggesting dif. bikes, ill help yah a bit more.
like said, you really have to know what you wanna do. if you dont, go borrow an XC bike, and go ask a friend to take you on an XC ride. then see bout riding some lite downhill, and maybe some urban or something. my guess, is if you are into newschool skiing, freeriding will be your focus. and that doesnt mean you cant still go ride a bit of XC, or street, etc.
i would highly reccomend buying a hardtail, as they teach you proper riding techniques, and really force you to be a better rider. plus, they can be very versitile. they are also cheap, and alot easier to maintain (suspension brings alot more headaches than just keeping pivots tight)
one of the most important factor in a bike is the head angle. this is the most important, but not the only factor deciding how it rides. the steeper the angle, the more maneuverable at slow speeds it will be. if your plannin on DH or real high speed riding, a slacker H.A. will make it more stable. if you can get something with an adjustable travel fork, from about 4-7 inches of travel, or something in that range, you will be able to ride just about everything fairly well. Check out MTBR.com, as there are shitloads of reviews, forums, etc. but remeber, plan on spending at LEAST 600 bucks for a fairly used bike, and min. 1000 for a new one. but if you can afford it, spend the money if you can.