Ipod Trouble - Ipod Experts wanted plz

Does anyone here know any websites that have mp3 tunes that u can download? What about programmes that can convert mpeg4s to mp3s? If u do can u plz let me know because I brought a MP4 player, and Breezsha brought a like-Ipod Shuffle from Trademe (will put a good word for them later) and we are having a bit of trouble with either converting them from mpeg4s to mp3s or downloading mp3s from a website that doesnt work. For example, my mum downloaded 4 the family the song Loyal with a wmp format, she put it on my Mp4 player, it showed up but the problem was there was a system error. We have I-Tunes but they r mpeg4s not mp3s so that is the reason why we want to download a system to turn out mpeg4s to mp3s.