I knew it was only a matter of time until they started developing these for portable media players; they've been working on laptop batteries for quite some time now. This is only a prototype, though, & we've yet to see those mystical laptop batteries, so take this with a grain of salt...

"Samsung reported that a 1.5-watt player can run up to four hours on the replaceable methanol fuel cell cartridge. The company plans to commercialize the cell by 2007 or 2008, according to a company spokesman."