http://pv3d.org/2008/12/28/click-then-tween-camera-to-plane/

see this first

http://pv3d.org/2009/01/11/tweening-rotated-planes-to-you/

similar things

http://embots.dfki.de/doc/seminar_ca/Kremer_Quaternions.pdf

the concept

http://en.wikipedia.org/wiki/Quaternions_and_spatial_rotation

wiki