There are several "zip" algorithms - The most popular on Windows is pkzip, which used to be a DOS program. Default ending is zip. Most popular on Unix, however, is gzip, ending .gz or .gzip. Often used together with tar, resulting in a .tgz or tar.gz ending. New and upcoming is bzip2, ending to .bz mostly. The fact that they all are "zip" compression causes some confusion. What we need to know is that Poser compresses using gzip. BTW, my recommendation for Windows is getting version 6.0 of PowerZip, which is IMHO better than WinZip and free.