I've got a SanDisk 1GB SD card in mine, works fine. Didn't do the "FAT/FAT32" as Booster describes, just dragged and dropped the folders over from local drive to SD card, the folders having been set up as Booster describes. I used itunes software to "rip" the files off the CD's, it creates its own folders in "My Music" in explorer, where you can just drag and drop as your leisure.
When I get bored of 10-11 albums on the SD card, I can just delete the files and load fresh music from my library onto the SD card.
I did buy another 1GB SanDisk card on eBay the other day, it was cheaper than the normal sources, but when it arrived, it was an "import" and would not work on my PC. I could get data onto it, but the head unit in the car came up with data error, so I sent it back. I would advise that you purchase "geniune" cards to ensure reliability. I got mine online from "L8shop"
Funkycat.