It's fully installed, and would play when I have a game running through Steam
http://store.steampowered.com/
in the background... Which is what really gets me, since there should be no program interaction between Steam and Koihime.
I really should just get the game somehow, but since I really have no plans to go to Japan anytime in the forseeable future, I'm not even sure where to start to get it at a reasonable price.