I've heard of Ouendan many times before, though I've never played. But, I do remember stumbling across a PC clone/simulator that was inspired by the series.
From what I read on the site, it's sorta like Stepmania, since you can make your own beatmaps for songs and upload em for others to download. You use your mouse to play instead of a stylus and there are rankings online. I might end up trying it out to kill time, so if anyone else's interested, you can dl it here:
osu! - rhythm is just a click away