There is a "copy photo" command in the dropdown that appears under each photo, but that physically adds another copy of the photo to the album you also want the image to appear in.
I don't think there is a way around it that anyone has come up with - but G2 will allow albums to share the same image (I believe). That's a ways away however as G2 is still under development.
As for your "highlights", there isn't a current way of doing that (there is the random photo hack that shows one pic at a time, and another hack that shows most recently uploaded, most voted etc). If you are thinking you'd like it as a feature for G2 you might want to mention that in the G2 thread.
Gaile