Then as I said above I wouldn't. ASCI miners have took over bitcoin. Using a GPU to mine will cost you money. Litecoin doesn't have this problem so look into that instead.
Edit: Make sure you read this article. It's ~4yrs old now, but the info still applies. Depending on the value of a coin it either is or isn't profitable. You'll have to work out your own MH/w info and see if the value of a coin is worth it or not.
http://www.tomshardware.com/reviews/bitcoin-mining-make-money,3514-8.html