ive been playing tf2 for a while on the ps3 and  resently ive traded the orange box   for ps3 in order to get it for pc   and ive started playin it properly on pc. im mainly a spy class but sometimes play as a medic or a scout. im trying to get the new equipment  for these classes but every time i go to a dropped item i want it disapears and doesent go into my invetory. i know that you can get them  by getting achevements  but i dont know wich ones. i got the upgraded medic gun compleately at random  with no medic corpses around anywhere and i was playing as a spy at the time, does this meen that they all are compleately random or can any one tell me exactly how to get the stuff for spy scout and medic

It's completely random. The more you play the more likely you are to get a weapon/headgear.

Just play the game. The longer you play the more likely you are to get a weapon, according to Valve.

Yep, you get them completely randomly.