RE:2 voices 2 characters...Yes, you can do it in version 1.38 but it is hard. You can animate more than one character with Poser and PoserSpeak. Just select each figure and animate their heads seperately in PoserSpeak. Then, you will need to join all the speech wav files into one master wav file b/c Poser only allows one sound file per movie. This will require a third party sound editing utility which allows you to record one wav file over another making a master sound file. This master sound file can then be imported into your Poser movie and animated with all voices together.
BTW, doing this is PoserSpeak version 2.0 is much easier. PoserSpeak combines the wav files together for you automatically.
RE:RE:2 voices 2 characters now in version 1.51...You can now do this is version 1.51 available now. You can also mix several voices on-top of each other, overlapping each other or one after the other. No limits to the amount of voices or types you can mix!