I use windows media player to download music to my mp3 player... but if I delete the music from the library on the media player... the next time I plug my mp3 player into my computer it deletes all the songs from the mp3 player... how can I stop this from happening?

Go to "My Computer" or simply "Computer" and the drive that's labeled whatever the MP3's name is (assuming it's F:\, but it could be E:\ or so forth) double click the icon. When you are in the MP3's folder, if there is a "MUSIC" folder there, place the music inside the "MUSIC" folder. This is what I do with my 8Gb Sony Walkman because I don't like the software that comes with it.