I tried to track down the same book when I did my bike trip over to Iceland last year but was not able to find any copies. Links to the author's web site appear to be out of date.
Just get a copy of Lonely Planet's guide to Iceland and a good road map.
I found a good map on Amazon "Globetrotter - Travel Map - Iceland"
Map shows a lot of of the jeep trails through the interior of the island.
There are a number of good ride reports on Adventure Rider forum
to give you an idea of what to expect over there.
Its great place to visit.