Yeah the original is free to download and you can play all aspects of the game. However, I think it only works for macintosh. Not sure though. Its a great game that everyone should check out.
I know a lot of you are looking for good games out there to play while you're patiently waiting for Diablo 3. Well, I've been playing this game for quite some time now called Escape Velocity, and I find it very entertaining. It was only for macintosh computers, but I think it has since expanded to PC. If you are interested in playing it is Free to download.
To read more about it go here: http://en.wikipedia.org/wiki/Escape_Velocity_(computer_game)