You can get the enemy Intel in campaign. Where there will be hidden and you will have to search for them.
Nothing really, they just unlock achievements.
http://www.supercheats.com/guides/call-of-duty-4/Intel-locations.shtml This website will explain where all the enemy Intel units are in the Call of Duty 4 campaign.
go on youtube type call of duty modern warfare 2 enemy intels
I think you can get them by finding some hidden enemy intel, at least that's how it works in Call of Duty 4: Modern Warfare.
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The intel items in Call of Duty: Modern Warfare 2 only unlocks trophies (PS3) or achievements (Xbox 360) when the player has collected 22 and 45 of the intel items. Unlike Call of Duty 4: Modern Warfare; collecting intel items do not unlock cheats for the single player campaign.
you get unlimited ammo
There are multiple enemies in Modern Warfare 3. They are Makarov, Volk, and Warrabe
Prince Farhad.
ENEMY
Do the challenge "Ultimate Sacrifice" which you unlock be nuking the enemy while you are losing
They are laptops hidden in most levels. in first level, look at the crates across from the watch tower near the pit to see the first one.