There are probably a number of books on the early days, when SJ and BG
were starting up--this also has some good chapters on Gates growing
up--Allen and Gates riding their bikes to critique computer programers at
a large company when they were 123 and 15 and later. I have a few, and
they help me get perspective since I wasn't using computers in those early
on times like many people were, but you'd probably enjoy this if you
haven't seen it (in paperback and sometimes in the used stores):
Fire In the Valley
http://www.fireinthevalley.com/
CH