On Modern Warfare 2, you earn weapons for multiplayer by achieving higher ranks in multiplayer.
At level 4 you can start creating classes then you get a new weapon every couple levels.
All you have to do is simply level up, i'd reccommend TDM or SnD :) also use the UMP45 to get easy kills :)
You unlock guns at certain levels but you must purchase them in order to use them in game. After you prestige, you have to repeat the proccess from the beginning.
Just kill people
Yes, there is online multiplayer on Call of Duty 4: Modern Warfare.
you have to get kills on your friends or on wifi the more kills the more guns
There are no golden weapons in Modern Warfare 2.
U go to multiplayer if no multiplayer u beat
Call of Duty World at War, Modern Warfare, Modern Warfare 2, Black Ops, and Modern Warfare 3 all have online multiplayer.
Yes You Can
The related link lists and described the weapons used in Call of Duty Modern Warfare 2
Unfortunately no, you can't play multiplayer on Call of Duty Modern Warfare 1 or on Call of Duty Modern Warfare 2 on the same screen. But on Call of Duty Modern Warfare 3 and Call of Duty Modern Warfare Black Ops you can play multiplayer on the same screen. There is an new Call of Duty Black Ops 2 coming out soon though, so I expect that to also have that feature, since its newer.
There are a total of 70 levels (ranks) in Modern Warfare 2 Multiplayer.
Sadly no.
No you can't.