I thought I had psycopg2 installed on my mac.. Thought.. But now I actually have!
After a quick search I found the right solution here. It only needed a little bit adjustment as I don’t use PostgresPlus, but just plain PostgreSQL.
To install, type the following in your command line. (Note that I use PostgreSQL 8.3 here! For different versions, different folders can hold, like /8.2 instead of /8.3 for PostgreSQL 8.2 for example).
PATH=$PATH:/Library/PostgreSQL/8.3/bin/ sudo easy_install psycopg2