Poser comes with both the Morph Brush and magnets.  PhilC has a number of tutorials on his site PhilC.net that show you how to use magnets to create face morphs. 

Sixus1 has a tutorial for sale here at RMP on using the morph brush and I believe Fugazi has a shorter one as well as the full Poser tutorial set.  Also check SMS Poser website for tutorials.

You can also use the various morphs that are in the V4 Morphs++ pack and others to create you face morph.

If the morph is for you own use, find an available morph that comes close to what you are looking for and use the various tools to fine tune it.