You need to track down the person who owns the rights and ask them. That can be tricky if it's an old book that's out of print, but for books that are still in print, start with the publisher. In some cases the rights situation may be so complex that no-one even knows who has them; a friend is in that situation at the moment, and believes she's optioned them from the right place (the author's estate), but can't prove it.

Note that if it's a popular book the rights have probably already been sold to some production company anyway.

Mark,

Thanks for the advice. Yeah, I'm leaning toward older books that are a bit lesser known, but nothing too obscure. Is there any sort of "standard" compensation (e.g. $1000 for 1 year) that you recommend to bring to the table at the beginning of negotiations? Or does it vary based on the authors'' popularity? I'm guessing the latter.....

Thanks again.

Robert Hestand, Lead Composer
http://www.royaltyfreescores.com

If it's not well known then $1000 for a year would probably be fine. But it could be anywhere from $1 to $1,000,000 really, depending on how popular the book is and whether the owner even wants to sell the rights.