The only utilities you need to deal with any Poser 5 or 6 content are to decode the RTE and PCF formats (both are ways of distributing modifications to commercial meshes such that they can't be used unless you have the originals). MacConverter handles (most) PCF files, but you can also use the Free Mac port of Objaction Mover (http://www.lamarchefamily.net/nakedsoft/) if you run into them. RTE files are more common, and can be decoded cross-platform by RTEJava (available in free stuff).

Optionally, fmorgan's McPBrowserPRO (or the free subset) will convert old RSR files into modern PNG previews. (The "pro" version provides some minimal but useful library management functions, as well as an easy content installer.)