If you can FTP/ssh/webdav into your webspace you should be able to install any software that you download provided:
- Your server meets the System requirements needed for the software, e.g., right version of php loaded, mysql, imagemajick, adequate space, etc. Many commercial companies will already have the basic requirements of most opensource products.
- You have setup your database (and assigned the proper permissions to the admin user) if the installer script does not do that part
- You have assigned correct permissions (chmod) to the correct folders so the installer script can write to them
- The software is not buggy (especially true for early releases, tests, demos, etc.)