Joining meshes from one object to another

I have a rather complicated model I’m working on. Lots of objects, lots of meshes etc.

Suppose I have Object A which has loads of meshes. I add to this and mess with it until I get it right. I want to remove these new meshes from Object A and call it Object B.

Suppose I have Object C and I want to add B to C. How can I do this? I am Blendering with v2.48a BTW.

Many thanks.

To remove part of a object, go into edit mode, select the virtexes and press P.

To join two objects select them and press ctrl + J