How can I disable the notification sounds while playing music?
First install Quick Settings: http://www.appbrain.com/app/quick-settings/com.bwx.bequick

With that under volume control you can control the following volumes seperately:


ringer
notification
media (this would control the music)
alarm
voice 
system


On top of that you can install Quick Profiles

...which will let you create a sound profile with the settings you want and easily activate it with one click.