I have a 99 sun fire and i have the same problem you have with the high piched noise. In mine the bearing was going out, I did some shopping around and found that you cant just replace the bearing. you go and buy a whole new AC set up for about 401.00 and if you get one of those hanyns books it tells you how to go about installing and un installing it. if you dont have the money to do that right now just go to your local auto parts store and get the shorter belt that by passes the AC, this will keep the noise from happening until u can get it fixed
hope this helps