Ronald,
You may also want to try A Natural History of the Reptiles and Amphibians in Sabah by Inger and Lian and the Systematics and Zoogeography of Amphibia of Borneo also by Inger.
As for snakes I think the best guide is the Snakes of Borneo by Stuebing and Inger or the New Holland Guide to snakes of Borneo.
There is also a pocket guide to the Lizards of Borneo by Das.
Maybe my girlfriend is right and I have too many herp books
Enjoy Borneo, I loved it.. fantastic herps, birds and mammals.. but be careful, I got malaria.. which is pants...
Cheers
Paul