advice, python for binary to xml

[noydb]

I'm looking for knowlegde about how best to go about converting a binary file 
(from a GPS unit) to GPX/XML.  I am completely clueless on this, so any 
start-from-the-beginning info would be greatly appreciated!  I'm guessing the 
level of effort will be huge?
Python 2.7, Windows 7
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