useragentstring.com has browser and OS information for its user agent strings. There's also an 'analyze' box to submit your own string. I don't know how easy it is to hook up to automatically, but it seems to have the sort of info you want.
Update from Original Posting (don't want to steal your upvotes):
I got this back from the author of http://useragentstring.com/:
I have a simple API, but I'm about to
recode a lot of my site, so it might
change in the near future. If you link
to my site, you can send a
useragentstring in a form field or in
the querystring with the name 'uas':
http://www.useragentstring.com/?uas=Opera/9.70%20(Linux%20i686%20;%20U;%20en-us)%20Presto/2.2.0
this will automaticly parse the
string. if you add &getText=all
http://www.useragentstring.com/?uas=Opera/9.70%20(Linux%20i686%20;%20U;%20en-us)%20Presto/2.2.0&getText=all
you will get a text file with key
value pairs like
agent_type=Browser;agent_name=Opera;agent_version=9.70...
