Back when I payed major attention to Windows CE, I did see several products designed to allow a CE machine to use a HD. I don't know if any of them are still around, but
http://www.windowsce.net used to be
the resource.
With the new generation PocketPCs, this should be no big deal at all. They have USB ports, and I'm sure that CE drivers for certain USB HDs are available. I'd check with Socket Communications at
http://www.socketcom.com
If this works, it would be amazing. My HP660LX boots in about 0.3 seconds. While the sound is not great, the new devices come with 16bit stereo and line out jacks...Very cool....And the touchscreen would just be neat.