>   Do you know of an interface to the Media Player?  Or how Sound can be
> coerced to play a large file?

I'm not sure what you're ultimately trying to do, but when I want to
control media playback from Ruby on windows, I usually use mplayer. 
It's easy, and mplayer has a ton of commandline options.

But, like I said, I'm not really sure what you're trying to do...