How do I GPU mine with only one GPU, which I'm currently using for graphics? Does that require going headless? How do I go headless?
I would recommend first checking this list to see what your expected hash rate will be:
And then see how much you will make from that rate:
Please factor in power consumption. After you have made a decision to mine armed with those facts, I'd join a mining pool and download GuiMiner.
The pool operator will be happy to address your questions on how to setup the mining client as you are making them money.