As far as I can recall there have been 3 Service Releases for Poser 6 so I would check by eFrontier and download and install those to be on the safe side.

You need to uncheck use Binary Morphs (this in the general preferences ???  I think that's what it is called) menu.  Saving a pz3 with binary morphs checked tends to cause the pz3 to be corrupt.

When you say you have put the text files into Poser 6 Textures what do you mean by this?  I'm just a little confused as to which files you've put where.

Have you tried reinstalling V4 to your Poser 6 Runtime and then not relocating any of those files and see if that clears your problems up with the missing head morphs and texture files?