Hello!
I recently met a guy from Poland who is working on a PCMCIA - USB Host card. He has already built the hardware and currently works on a Windows 98 driver. If somebody is interested in the project: https://github.com/korneliuszo/pcmciahost/
Maybe we can also write a driver for Windows CE and Linux!
Japanese CF USB Host Card, (Ratoc Systems) has the REX-CFU2 that supported WM6.0, WM5.0, Windows Mobile 2003 SE and Windows Mobile 2003. Maybe it can support MP900C / Sigmarion 3?