Amazon confused me. Says "Sorcerer in the North (Book 5)" is in paperback there. It also says "Sorcerer of the North (#5)" is due out in hardcover in Nov. '08.
http://www.johnflanagan.com
This just led to a domain for me at this time. It may not, for you, and may lead to an explanatory author's site.
Otherwise, suggest you check out all the books and reviews etc. on Amazon (link on top) to see which is which there, and what is what.
Good luck.