No, the book is not available in paperback edition yet and it won't be available in paperback until Novemeber at the very soonest since it was just published by Baen Books. Check their publishing schedule at
http://www.baen.com/scheduleXML.asp . You'll find The Shiva Option in February and you'll see that the schedule is set until September and no mention of a paperback edition of The Shiva Option. So unless you're capable of waiting that long hardcover is the way to go.
And yes, David Weber was closely invlolved in developing the tabletop game Starfire, specifically the 3rd edition if I remember correctly. His Last official starfire product was ISW-4:Arachnids.