How Do I Enable Gnome Sound?

[Ed Sutherland]

I'm using Gnome 2.2.0 and want to play MP3s and CDs. I thought I enabled sound 
by going into Preferences->Sound and enabling both the sound server and 
system sounds. I'm getting system sounds (the little .wav files for certain 
actions) but I still cannot play MP3s or CDs (I know I must use xmms-cdread  
to play CDs on the iMac.)

What am I forgetting? (I have turned up the volume and speaker settings in 
Sound & Video->Volume Control.)

Thanks.

Ed