I might have misunderstood something but it was my understanding that jmo707 can export the card and that Linux can read it but Windows can't. If that is the case, then the problem must be in the way the card is partitioned and/or formatted.

Another problem I had in the past was that Windows at some point decided to simply not recognize my N900 as an external storage. I rebooted the same PC to Linux and could read from.write to the phone just fine. Reboot again to Windows, no dice. If I remember correctly, I fixed it by replacing the USB cable. Windows was somehow more fussy.