I'm searching too....
I have a SanDisk 256MB+WifFi card, and I want to use it in my SD Slot in a Compaq nw8000 Notebook
(Fedora 2 + homeBrewn kernel)
What i've found now :
* Linux has MMC drivers (Same Physical Format as SD cards)
* Most SD Cards are accessible with MMC Drivers
* SD Cards have an Security layer inside the card (If I understand the the Documentation correct)
* How to acces an SD Card is not Public, but :
* The Geeks at Fujitsu are working on a SDIO Driver for Linux
* Access to SDIO devices is not the same as accessing SD storage
hope, I find something more useful ...