user4334: 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?

user4070: I would recommend first checking this list to see what your expected hash rate will be:
https://en.bitcoin.it/wiki/Mining_hardware_comparison
And then see how much you will make from that rate:
http://www.alloscomp.com/bitcoin/calculator
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. 
http://guiminer.org/
http://mining.bitcoin.cz/
The pool operator will be happy to address your questions on how to setup the mining client as you are making them money. 

4334: <p>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?</p>
 4070: <p>I would recommend first checking this list to see what your expected hash rate will be:</p>

<p><a href="https://en.bitcoin.it/wiki/Mining_hardware_comparison" rel="nofollow">https://en.bitcoin.it/wiki/Mining_hardware_comparison</a></p>

<p>And then see how much you will make from that rate:</p>

<p><a href="http://www.alloscomp.com/bitcoin/calculator" rel="nofollow">http://www.alloscomp.com/bitcoin/calculator</a></p>

<p>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. </p>

<p><a href="http://guiminer.org/" rel="nofollow">http://guiminer.org/</a></p>

<p><a href="http://mining.bitcoin.cz/" rel="nofollow">http://mining.bitcoin.cz/</a></p>

<p>The pool operator will be happy to address your questions on how to setup the mining client as you are making them money. </p>
