If you're specifically looking for a book with diagrams and descriptions, you might try some of the books authored by Paul Bottomer. I got a copy of a book, I believe entitled "Let's Dance!: Learn to Swing, Jitterbug, Rumba, Tango, Line Dance, Lambada, Cha-Cha, Waltz, Two-Step, Foxtrot and Salsa With Style, Grace and Ease," through my local public library. Despite the exhausting title, the book actually covers several more dances as well, including a few basic steps of Paso Doble. The book is a hardcover, oversized edition of some 200-300 pages, lavishly illustrated with both "sequuence stills" of couples dancing and a many "foot-patterns" as well.
The downside may be that the book, and so far as I know, virtually all of Bottomer's books, are written for the International or Club Styles, not American Style.
Most of the steps provided are very basic (for all dances, not just Paso Doble). If you're unfamiliar with the dance, you will also miss a lot that simply doesn't fit well into a "book" format. I'll agree with Mallee that a video will give you much more of an idea about the stylistic requirements of the dance than this book will. I'm familiar with the Dancevision tape Mallee (hello again!) wrote of, and I'll echo her endoresement (though personally I find the persona adopted by Corky Ballas to be "a bit much"). If you've never bought from Dancevison before, it would make financial sense to buy a second (more expensive) tape to capitalize on their Introductory Offer.
Doing a few quick serches:
Dancevison Intro Offer and Tape description:
http://dancevision.com/buyers_guide/shopping_guide/hot_deals_specials_promotions/59/http://dancevision.com/store/videos/browse_by_instructors/corky_shirley_ballas/international_latin_syllabusfigures/ISCB39/If you don't have an up-to-date browser, you might have trouble accessing the Dnacevison pages. I found something on Amazon that I *think* is the book I described; in any case, I've made the title I gave up conform to it!
Good luck and have fun!
R