Retrieve a list of browsers/agents installed in client system
"Scanning" a client from a server may be possible if you break their security or get them to break it for you through some extension (see windows udate, for example). Either way, it's evil.
I would like to write a web application (in django) which scans the client/remote computers (assumption is windows) and retrieve the list of software's(mainly browsers) installed. Looking for suggestions to implement it.

Is this possible without asking the user to download any scritps/exe's?
If so, is it possible via java script?

I am planning to use python/django to write the entire app. Any input would be much appreciated.
EDIT : Comments on feasibility in java also much appreciated