Has anyone tried to acquire rights to a story someone else wrote? We're interested in adapting a series of books for an adventure games series, but we don't know the first thing about rights, royalties, or negotiations. Anybody been there?

I haven't actually done it before, but my first step would be to contact the publisher and ask them wether they own the rights to the book or wether the author still has control of what is done with the books.

Then contact the controling body/person/agent and explain what you want to do preferably with some sort of example of stuff you've done to show that you and do it etc.

If the series is old enough, make sure it hasn't become public domain yet. If it's public domain, you don't have to worry about the rights.