NeaP4 does indeed require RTE encoder to install.
In order to clarify for iampan69, in the early days of
Poser, there was no way to distribute modififed characters because there was no way to strip the original geometry of the character from the file. Distributing any part of someone elses geometry file is considered a copyright violation. So a way of legally distributing these files was figured out and a program called OBJ Mover could transfer geometry stuff legally. (RTE encoder does the same thing)
The requirement to use it was that you had to have the original mesh that the modified mesh was based on. In this case the P4 woman (original mesh) and NeaP4 (the modified mesh information. Since the NeaP4 obj (geometry file) is based on the original P4 woman which is copyrighted by
Poser's copyright holder, NeaP4 cannot be directly distributed as created. So RTE encoder codes the file in some way and allows distribution.
Later on a way was discovered to use file pointers and geometry swapping (among other methods) that did not require special coding. But occasionally this special coding method is still used as it was with NeaP4.
RTE Encoder can be downloaded from this page. I think the readme file or documentation will walk you thru the conversion. If you have any questions, anyone here should be able to help. Just ask.
http://rtencoder.com/downloads