what stuff??

zpin Posts: 14
edited January 2011 in MTB beginners
right. i am looking to buy a mountain bike. fairly cheap, second hand, but will get me up and down hills with some fun, keeping up with the mates. Being a roadie, i feel like delving into the dark side occasionally, but i don't know what i'm buying, so help please. also, what size frame? i'm 6ft2 with an inside leg of 34.
many thanks :)