In that case you might need to try the brute force technique.
First go to http://mirror.internode.on.net
and find your way to pclinuxos/2007/main in its public mirror space. Then download the current version of pgadmin3 to make sure you have it. Make a note of the path to the file.
Then open a console and su to root. Type "rpm -e --nodeps pgadmin3 && apt-get install <path to file>/pgadmin3"[tab] [Enter]. If the path is xcorrect it should autocomplete when you press [tab].
If apt-get still complains you can try installing with "rpm -ivh <path to file>/pgadmin3"[tab] [Enter], but that might fail due to dependencies.
Whatever happens I would then try "apt-get update && apt-get dist-upgrade" again and if that complains of broken packages, "apt-get --fix-broken dist-upgrade".
If the problem persists, it's getting difficult!