The short question is: will I succeed in installing/upgrading a Woody program on Potato, or will it give me troubles?
Answer: I did this with SANE. It worked. Just include the proper Woody sources line in your sourses.list, apt-get update, apt-get install <program here> I would imagine that the Debian dependency tracking system takes care of things fitting nicely together. Mind you, nothing in Woody is tested to be stable, so it's at your own risc. However, on and off I have seen people saying that their systems are Potato-Woody mixtures, so others seem to have success with this also. I have no experience with Gimp 1.2 or phpmyadmin. You are on your own there. Cheers Johnny :o)