Yes, you need Poser in order to use a pz3 file.  

The best way to test Vue is to try it out on your computer.  The free PLE version is not time limited or "cripple" software.  It is locked to your computer (files can not be opened in any other version of Vue or other people who have the PLE version) and the render has a watermark.  other than that - it's a full version of Infinite or xStream if you want to test how is works with programs like 3D Studio or Maya, etc.  

http://www.e-onsoftware.com/products/?page=try  Link is at the top of the page.

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