Chairs don't seem to have a solid enough surface to sit a unit in--when setposed onto a chair, the units fall through it or slide off it. But they will sit on benches, and other objects (tailgate of truck, wall, etc.). You have to experiment.
I put the following code in a Talk waypoint for a unit to get him to sit on a bench (see first pic):
dostop this; this switchmove "Truck_Cargo02"; this setpos (chairA modelToWorld [-.3,-.1,1.3]); this dowatch (this modelToWorld [0,20,30]);
It's the cargo animations called by switchmove that give you a sitting animation. There are many to choose from. You then SETPOS the unit relative to the object. In the above case I placed a bench (Sitbank 1 object) and named it chairA.
The second pic shows 3 guys sitting on an ammobox using two cargo animations and the "AH6_Gunner" gunner animation (the guy holding his wanker).
The move animations can be found here:
http://community.bistudio.com/wiki/Armed_Assault:_Moves_List#Acts...
One TV man sitting animation is: "ActsPercMstpSnonWnonDnon_MarianQ_TVstudioMan_Loop1"