If it helps, I started a similar project a few years ago on SourceForge when I was just learning python called python2xlw. I haven't supported it for quite a while, however, I still use it a lot in my own work.
I needed to create Excel files with scatter charts in them for a web interface so I went through the excercise of disassembling the BIFF codes of the older XLW format of excel and creating a byte stream representation of the spreadsheet that could be saved to file or sent directly to the web user as an excel application in there browser. The newer XLS format is a bit more complex and I didn't have enough documentation to create the charts I needed directly from python in the newer XLS format. (the current version of excel still understands XLW, however, so you're just a "SAVE AS" away from XLS.) As I think was mentioned in another post, you can create charts etc. using the COM interface for a client-type application, however, my goal was to create them on-the-fly directly from the web server without launching a server-side excel application. There is a nice Perl project called Spreadsheet::WriteExcel that John McNamara created that was very helpful to me at that time, however, it only created the worksheets, not charts. -- http://mail.python.org/mailman/listinfo/python-list