Arabic letters

Hi,

I wonder if there is a website where one can listen to sounds of the Arabic letters being pronounced.

Right now many letters just sound all the time to me when my Arabic teacher pronouces them in class (for example, س and ص sound just the same to me), so I figured it might help if I could listen to the letters again and again and directly compare them. The CD that comes with our textbook doesn't have anything like that.

Thanks!