Unzipping Problem

Folks, we exchange CAD data with an automotive customer through Odex professional on windows 2003 server. The files come in .z format which we extract but the extracted files do not have a format on them.

I can see from txt file that comes with the data that they were compressed using gzip so I add .gzip to extratcxed files but when try to extract them again with winrar I get no archives found in selected files. I have been searching the web but can't find anything on this? Derek.