TimeTo™ will run on Macintosh computers using a Windows emulator, such as Parallels Desktop for Mac (OSX 10.4.6 or higher) or Connectix Virtual PC.
How to use Parallels Desktop to run TimeTo™ on your Mac, side-by-side with Mac applications: http://www.lifehacker.com/software/parallels/hack-how-to-run-windows-end-mac-apps-sidebyside-with-parallels-221002.php
Another option is to use Boot Camp to run Windows XP on your Mac, then
run TimeTo™ from that.