How do you structure a Python application inclusive of unit tests?

I’ve seen a variety of application structures out there just browsing some projects on Google Code. I’ve also read the docs on http://python.org regarding the use of the unittest package. My problem is that I want to have my app structured something like this but I can’t for the life of me get the pathing to see the modules in my source directory. I’d rather not have to put the tests in with the actual code but I’m not sure how to get those tests to run when they can’t import the modules I need. Please forgive my ignorance as I’m just beginning with Python.