Good luck figuring out how to charge the ipod battery and installing it, etc >__<
Seriously. Most of those iPod batteries use LiPoly cells, which are much harder to charge and need an even more specialized charging circuit than the one I picked from Analog Devices that can charge LiON batteries. Then again if you were really determined you could go through the iPod and find the charging circuit and buy whatever chip it's using to do it.
After Sony's big battery recall, I will never buy a Sony battery again. Ever. The battery pack I designed for Chumby uses LG batteries that are pretty industry standard for making battery packs; they're smaller than InfoLiths and cheaper to boot. I'm currently working on the PCB design for the charger, but I've been stalling to wait for the schematic for default daughtercard to become available so I can integrate the charger with it. I'm also working on breadboarding the prototype charging circuit but I haven't had any time to work on it yet this week.
For more information, check out the Power thread in hardware, I'll post everything I'm working on there.