Odd my copy of Winzip unzipped the file without asking for the file extension & got the file extracted properly with extension.

Here's how I tested it, I copied the ppz file to a temp folder, added .gz to the end of it, double clicked it which started winzip, hit the extract button on the toolbar, chose the folder & hit ok, cue creation of a fully working expanded pp2 file.

Windows 7 64Bit
Poser Pro 2010 SR1