Follow the link on the previous page (or here) to The Music Interactive's Download page.
Click on the icon next to Staff Wars V1.3 (circled above) appropriate for your operating system (the left for Mac, the right for PC.) If download does not start immediately, you may need to select Save, depending on your browser choice.
Open the compressed folder StaffWars V1.2
Open the folder for your operating system (top MAC, bottom PC)
Open the file StaffWars
Select the Run option. If another dialogue box opens, select Run as well.