>> There was an article in CircuitCellar (see
>> http://www.circuitcellar.com/magazine/176toc.htm "Portable FAT library
>> for MCU Applications").
>> I bought the article ($ 1,50) and it contains a FAT filesystem interface
>> towards an SD/MMC including source code.
>
> Additional MMC/Fat code can be found here:
> http://ulrichradig.de/site/arm_projekts/mmc_sd/index.htm
The Circuit Cellar version is much better.
MMC/SD FAT Library, ~1k in size:
ftp://ftp.circuitcellar.com/pub/Circuit_Cellar/2005/176/Sham176.zip