Planet Half-Life have had a chat with some of the people from Valve and its quite interesting it also strys twards the technical side of the source engine aswell

ColdW|SidewinderX: How will the weapon sysytem be set up regarding viewable models in1st and 3rd person view. Will the same mesh be used for both or will it use a system similar to HL1 with the _w _p system?
valve|gaben: Weapons have two models - the in-view model and the world model (seen in 3rd person).

You ca read the rest of this over at Planet Half-Life