I've Noticed in game play videos that it seems you can hold a primary weapon and a secondary weapon but on top of that you can hold C4 and a bunch of RPG ammo too?

Can someone clear this up for me please... i figured if you were to pick up the RPG ( i forget the name) it would replace one of your weapon classes?

The JAW isn't a primary weapon, it replaces your grenades in Multiplayer and in Singleplayer you can carry a few (they're one-shot each) along with grenades and C4.

ok thanks man. So if the JAW, C4, and Grenades are in the same category, they would all be switched with the d pad on a 360 controller?

Most likely, since in the default control layout (for the beta, at least), D-pad right cycles through explosives.