ogg files what are they and why can't I play them
 

Some songs I download don't show in Nero's list of files in my shared directory. On reclicking the file to download, it asks if I really want to replace "[name of song].ogg"? What is the ogg extension, and how do I get it to play?

Ogg Vorbis is one of many types of mp3. And yes your mp3 player will need a special codec to play it. For Mac, Audion will play it (no iTunes can't.) For Windows, QCD (free) will play it. For almost every other app that I'm aware of you'll need to obtain xtra codecs.