Noah's Classifieds can be downloaded in two different file archive format: as a zip file, or as a gzip'ed tar archive, often called tgz or tarball. This latter one is a very common UNIX archiving format. If you are a Linux/Unix user or at least your web server is hosted on a compatible OS and you have shell access to it, you probably want to choose the tarball. Choose whichever you are more familiar with. Here is how to extract the tarball in different Operating Systems.
Probably all of you can use the following:
tar -xzvf classifieds_x.y.z-RSS.tgz
This will extract the tarball in the current directory.
On some non-Linux systems you might find the GNU tar program under the name gtar, therefore use:
gtar -xzvf classifieds_x.y.z-RSS.tgz
If none of them work, you can still use the zipped archive and extract it this way:
unzip classifieds_x.y.z-RSS.zip
For Windows users, the zipped archive is the easiest one, but if you still choose the tarball, you might need to modify the .tgz extension to .tar.gz to make the archive tools recognize the file format correctly. To extract the tarball you need an extraction tool. There are hundreds of different programs available and there is a good chance that you already have one.
Usually double-clicking on the .tgz file will extract it. Since Mac OS X has a unixoid system under the hood, the description for Linux/Unix above works in the Terminal.app. StuffIt Expander version 8.02 and higher handles .tgz correctly. Earlier versions of Stuffit Expander may as well.