I believe this is what you want - I've used it in the past and am pretty happy with it....
http://www.softick.com/pocket-pc/cardexport2/
Biggest pain in the *** I've run into though: Anything you find out there isnt really using the Mass Storage device protocol (dunno the technical name for it) that you see with flash drives and card readers, and instead just using the slow as b*lls ActiveSync protocol to "fake" it to your OS.
Oh well. Good luck - hope that helped
jm