There are python packages available to work with Excel files that will run on any Python platform and that do not require either Windows or Excel to be used. They are fast, reliable and open source:
This package is for reading data and formatting information from Excel files.
This package is for writing data and formatting information to Excel files.
This package collects utilities that require both xlrd and xlwt, including the ability to copy and modify or filter existing excel files.
The notes for the tutorial which covers all three packages can be downloaded here:
These notes also make a pretty good reference for the three packages.
There is a Google Group dedicated to working with Excel files in Python, including the libraries listed above along with manipulating the Excel application via COM.
The following companies can provide commercial software development and consultancy and are specialists in working with Excel files in Python: