Kudos on the initiative. I think this is probably the most important bitcoin concept as far as gaining mainstream users. Imagine selling these at walmarts and supermarkets and Best Buys. It's impossible to secure the average joe's computer, so the bitcoin client running on a desktop or laptop will never be safe without something like this, but pick one of these up and you have a stupid-proof secure bitcoin device.
And how would an open source jukebox firmware help me?
The RockBox stuff would let you use one of the inexpensive $25 mp3 players as a platform. They already have displays and input interfaces. For the production version maybe you could get a chinese plant to rebrand an mp3 player.
If you want to build from the ground up, might be worth looking into a crypto chip like this:
http://www.maxim-ic.com/datasheet/index.mvp/id/7277It has built-in hardware ECDSA, which is what bitcoin uses to sign transactions, it has a true random number generator, and it's designed to be secure. If you can do this with a crypto chip, a cheap microprocessor and interface with a mobile phone or computer via bluetooth for an easier GUI, you might be able to get this really cheap and super secure.
I'm kinda looking into building from the ground up, the end device will cost a bit more, but that way nobody will be able to drop in and steal your bitcoins jut by plugging something into your device. The arm processor I have selected has a cryptography module in it, so I don't think a chip will be needed.
I was thinking about mainstream users when I though of this. If we can make a $25-$50 device (with a $50-$75 one with an easier interface, for the extremely not technically inclined (a.k.a. they think a *nix is a type of windows)), and make it locked down before it ever gets to them, there is no way they are going to mess it up.
