Poser 7 Revealed by Kelly L. Murdock is basic.  But always on My desk.  A new addition to the pile (of two) is Jeremy Birn's Digital Lighting and Rendering..   This book came very highly recommended from another thread..

If Poser 8 Revealed was on the shelves here in OZ.   I would take a long look..  hoping for a more (much) detailed rundown on P8's IDL system..