File extensions are crucial...

Previous answers are correct. Each operating system will open files of "its own kind."

*.msi files are to be opened and installed by Windows Installer...make sure that you have the latest Installer downloaded and installed.

*.exe files are self-executable in Windows...don't know about MAC or Linux

*.rar files are opened with WinRAR and if you downloaded a *.rar file that came with a key, then you have to have the key to open the bundle, to get at the *.exe file.

*.zip are opened with WinZIP and work, as above...sometimes you can double click on them, and off they go...

Text and Image files don't open because you have not set your in-house viewer to open a file with that extension... WordPerfect, Word, Works, Adobe, Adobe Pagemaker, and the list goes on...Irfan View, ACDSee...etc.

Each program often has its own proprietary extension. If you are really stuck sometime, open the file in WordPad...yes, I am aware of the gobbledygook that will appear...but look in the very first, top-most line of script...sometimes the program used to open it is written right there.

Experiment with the list of most common program extensions by changing them around...and sometimes they are just hidden zip/rar files under another name...