I don’t know if this is what you’re thinking of, but some notebooks/netbooks (though not the NC10) now come with a minimal Linux distribution on an internal chip, which boots very fast and can run a handful of applications (like web browsers, and potentially media players) with very little overhead and nearly instant access:
http://www.linux.com/feature/153130
You can choose whether you want to load your main OS (e.g. XP, or a full Linux distribution) or just the mini OS when you switch the machine on. But I don’t know if the mini OS would really save power in this situation (the media player itself would probably account for most of your power consumption).