[Psycho *BoB*]

open ur sig (psd), open ur pic (jpg/gif)

Now what I do is I make my sig screen
and pic screen small. Now in ur pic screen
select what you wanna ad to the sig
and then take the move tool and drag
the selected area to ur sig, and it should
copy the selected pic to ur sig screen.

Al least thats how I do it

Hope this will help.