I don't know about you, but I actually looked at WinCE as a possible platform for the distributed filesystem I work on. The development kits are pretty much useless for kernel level hacking. Besides, one of the requirements for WinCE devices is to have at least 32MB of memory, and I'm sure that car stereo had more than that (voice recognition is a memory hungry app) and wasn't doing anything else at the time.

You'll probably end up better off running PalmOS in a m68k emulator (i.e. pose) on an empeg. The screen size and depth are much closer (160x160x1 or 4), the available amount of memory is in the same range (512K-8MB) and the ARM processor is about 10x faster which compensates for having to emulate the 68K CPU.