First try to reformat the sd/mmx card in FAT16. This will offer up to 2GB and (in theory) 512 root entries. Any long filename (>8.3) and any sub folder will decrease the amount of useable files in root.
Personaly I use only 8.3 filename for all .adf image name and only one sub folder to store temp. unused adf images.
That will give about 240 useable .adf files in root (minimig1.bin and kick.rom must also be present).
Maybe the maximum amount of root entries is 256, but Im not 100% sure.
