Just click on the big red button that says "get it!" You have to do it twice in a row, after a second page loads. Don't worry about requests to donate, it's not required to download.
You get a zip file that you must unpack. If you don't know how you can check this tutorial:
http://www.abandonia.com/vbullet/showthread.php?t=17497
And then you need DOSBox to play, here's a simple tutorial:
http://www.abandonia.com/vbullet/showthread.php?t=17498