Air conditioning does not work in my car

I have a 2003 Pontiac GrandAM that I bought in May, 2006. It had about 50,000 miles on it when I bought it and the air conditioning worked just fine. The car now has 71,000 miles on it and the AC stopped working in April, 2008. In August, 2008 I noticed that the fan speed was broken. In other words, there are 5 fan speeds in which 1 is the lowest amount of air coming out (for heat or ac) and 5 is the highest. 1, 2, and 3 speeds do not work. I have to switch the knob to the 4 speed to get any air to come out. Keep in mind that the heat works fine in my car and I am well aware that the AC and heat in a car are separate from each other. I was told by a car dealer that it is my electrical resistor that went or was fried causing the fan speed to default to the 4 speed. I am not sure if this guy is right though. So, what would it take to fix this type of problem?

Also, the AC in my car clearly does not work. I was told it could either be the compressor that is broken or it could just need some frion. However, car dealers charge $75 just to find out what is wrong with my AC. Then they are going to charge a ton of money to fix it. My friend is great with cars, and he keeps telling me he is going to test it for me but never has yet. Is there a simple way to do this myself or someone who isn't going to charge me tons of money just to test it?