Code Problems

Today my coolant light came on. I drained and flushed my radiator, then filled it back up with dex-cool. It is definatley full, but the light is still on. I ran a test on my car and got a code nack that read the following way:
A/C Refrigerant pressure sensor a circuit malfunction.

Is this something I should bother with or should I just take it in and have someone fix it? If I have someone look at it what cost should I expect - I don't want to get ripped off.

. My car also has been stalling off and on while idling. I replaced one of my vacuum lines that looked bad, and it is running alot smoother, however when I ran the test on my car for the above, I also received the following code:
system too rich (bank 1)

I am under the impression this is an O2 sensor, but I don't know if it is the upstream or downstream from the catylac converter. Again is this something to have someone else worry about or should I attempt it. And how much should I expect.

This is for a pontiac grand am 1998 SE 2.4L

Thank you for your help.