This video describes how to use code completion in Aptana Studio, and consequently Eclipse with PyDev. Also, I recommend you download the IDE from the website even if you are using a Linux distribution with the IDE in your package repository as the ones in the repo tend to be outdated.
While this video describes the process under the Linux platform, the details should be relevant under other platforms through slight modification.
Aptana Studio homepage:
Also, for those of you still waiting for the preview window tutorial, that’s still coming!! I’ve been very busy, and that’s one that takes a lot of preparation, so I’m waiting for finals to end before starting. 🙂