At least four new or modified weapons have been confirmed that will appear in Modern Warfare 2. Screenshots on the forum of Infinity Ward confirms this. It has been also reported through ComputerAndVideogames about the multiplayer mode’s custom killstreak.
The details as of now are 2 submachine guns and 2 assault rifles. Three of these four seems to be brand new, which are similar to Call of Duty 4 guns, and one is supposed to be a modified version of a gun from COD4.
Tavor TAR-21 seems to the newest and most unusual-looking gun. Tavor TAR-21 is the latest Israeli-made assault rifle. Confirmation of the gun comes from a single shot of the multiplayer footage, but it there is no confirmation for the campaign or the co-op modes.
FN SCAR-H is the other new assault rifle. Till date it has been confirmed to be in multiplayer.
H&K UMP .45 is the new sub machine gun and it has been confirmed through the screenshots of the multiplayer footage and few campaign cut scenes.
In the game the players will be able to choose rewards from different lengths of killstreaks. Players who can save a 15-kill streak may be able to use the AC-130 gunship from COD4 where as a less experienced gamer might be able to use something smaller, but of course more often.