My biggest worry is losing stuff I need. How do I backup my itunes library. I am a worship pastor at a church and I can't lose my music. So how do I back all of that up? And then how do I reinstall

I'm having the same problem. My itunes app won't open, but also my mail app. won't work and safari. I'm using a Powerbook with Mac OS X 10.4.11. I've looked over another discussion and tried a few things. I've tried opening from applications folder....nothing. I've tried creating a new user account ...