I've been wanting an iPod for some time now, but need some answers before I invest. I'm debating between the 20 or 40 GB. Do iPods hold both AAC and MP3 formats? If so, this is my question... If I burn the same cd onto my iPod (ex. 13 tracks), which format will use more space? The website leads me to believe a 20GB will hold 5,000 songs. Is that in MP3 or AAC format? I just wanna make sure I get a big enough one. I listen to a lot of songs in the 10 min range, which would change that 5000 song estimate quite a bit. I wanna get the best deal for my money. Thanks!