Well, each picture is a layer.
So, you right-click on the layer in the layers palette and go "Duplicate Layer". I have Photoshop 6.0 but it should be similar, if not the same.
To bring two pictures together as if they were one, you could export the file as an image type that flattens the layers, as far as I can remember, the only file format that doesn’t flatten the layers is ps’s native ps file format.
OR within the program you can go Layer >> flatten image; or Layer >> Merge Linked if your layers are linked or Layer >> Merge Visible.
hth,
animgirl