I used to have trouble getting numpy and scipy installed - until I started using homebrew. It blows MacPorts out of the water. Just make sure your architecture is set correctly as Jesse outlines in this blog post, otherwise you'll run into problems building the various C components with gcc.
What he said; use homebrew - judicious use of homebrew and virtualenv will save you lots of pain. I never install framework builds from python.org - I don't like installing things into /Library or ~/Library
