Noel, go to this link and log on to your FoCal account.
Top line says "Already Purchased". You can download there. You can also add or take away camera serial numbers. You do not have to buy another copy.
http://www.reikan.co.uk/focalweb/index.php/purchase/

Reiken sold you the Windows version. You get to help them test the Mac Beta for free because you bought the Windows version.

Edit; I am getting a error message off the link the site is down. I was getting that earlier and was able to access Reikan by looking it up on Google.