I have a .Z or .gz file

ZipIt can only expand or create zip files - i.e., files that end in '.zip'. Files that end in '.Z' or '.gz', or any other extension for that matter, are probably not zip files.

In order to expand a '.Z' file, you will need a program called MacCompress. To expand files that end in '.gz', you will need MacGZip. Both of these programs are available from standard Macintosh archives, including Info-Mac at:

ftp://mirrors.aol.com/pub/info-mac/cmp/