Oh, the purchase box isn't on that link you provided. This is where I was led to:
http://www.nch.com.au/support/supportcontact.html?software=PhotoStage&support=http%3A%2F%2Fwww.nchsoftware.com%2Fslideshow%2Fsupport.html&pty=2&purchaseclass=photostage&dldwin=http%3A%2F%2Fwww.nch.com.au%2Fcomponents%2Fpstagesetup.exe&dldmac=http%3A%2F%2Fwww.nch.com.au%2Fcomponents%2Fpstagemaci.zip
Anyway, I already figured out how to make it work right.