Thats what I did with my creative zen jukebox. I switched out the 40 gig laptop drive with a 120 gig laptop drive. It can'tplay movie, only music, but I use it more as a external harddrive to carry movies to school.
To the suggestion at hand...
What would you need to do to make this possible.
1. A hard drive
2. Hard drive enclousure
3. A cable to connect them
4. A MP3 player that has some kind of connector for syncing music and possibly powering it to save on the use of batteries
5. a way to power the hard drive
6. either rewriting some of the MP3 players code to call the music from the hardrive or a external device to stream the music from the hard drive to the MP3 player.
Hard drives are really cheap so that is easy.
They sell portable hard drive systems like Think geek's which comes with a rubber protective sleeve a IDE or SATA to usb connector and a external power source so that takes care of numbers 2, 3, and 5.
I am sure that there are many MP3 players that have some form of USB port connector so thats a go.
