loud squeaking?

I dont know much about cars but i have a 1997 saturn SL with 75k on it and when i start my car i hear a loud squeak comming out of the engine. I pop the hood and i see its a belt but i dont know which one or anything about it. To get this replaced how much will it run me and is it somethingi can do myself?

DOHC or SOHC? There is only one belt. It is called a surpentine belt and will cost you about $20-25. if you have handy with normal tools you should be able to replace it yourself.