Models parts..

Ok, what I wanted to ask is how do I append a certain model to another model. For example, how do I attach a sword model to knight model, how do I locate the position where I want to attach it(sword). Or, for example, some of you so how turrets in Homeworld ships fire, they rotate independantly of animation. E.g I got 2 separate models, how do I attach one to another where I want to in 3D? Thanks all..