|128Kbps MP3s are what is officially supported, and work on all models. Some units can play >128Kbps MP3s properly, but others cannot. For <128Kbps (say, audio books) all the units I tried it on played the file too fast.|
The SD card needs to be formatted FAT16 (any variation, MSDOS, VFAT16, etc.). Supported capacity has come into question recently. I've personally played MP3s and videos off a 1GB SD card, but another user was reporting that his wouldn't play files off anything higher than 512MB SD cards, and appearently this is limited in the firmware of his unit. SD cards greater than 1GB will not work, as they changed the copy-protection scheme and dropped MMC compatability.