Simply Track Time uses the .Net Framework 3.5 Service Pack 1 so you need to have this installed on your computer before you can install Simply Track Time.
You can download the latest version of this framework from Microsoft at this url. (.Net Framework 3.5 Service Pack 1). Click the "Install it now" button.
After doing this - the Simply Track Time installer will run on your computer.
So simple steps:
Download Windows Installer 3.1 or later and install it - you may be prompted for a reboot.
Download the .Net Framework 3.5 Service Pack 1 and run the installer.
Download the Simply Track Time installer and run it.