I'm looking for a good overview of Tk concepts.

[Noah from IT Goes Click]

I'm comming from the background of being primarily a data processing 
programmer (Python) and I'd like to do some GUI stuff for a comercial 
project but I have quite a bit of time, nothing too complex but it has 
to work on Windows98+ OSX and Solaris so I was thinking Tkinter. I was 
wondering if there were some sites with a good overview of the whole 
Python +Tk shpeal, I've got some code examples and "Programming Python 
2nd Edition" but that's more of a learn by example, rather than an 
overview of concepts. Anyone have a good recommendation?