I believe if you use your Dad purely as a co-signer, you still will qualify for the tax credit... which is 10% of the purchase price to a max of 8,000.
It's a great time to buy, and there're plenty of discounted inventory on townhomes.
Also if you think that you score is above 580, there might be a possibility to go on your own; I could even get you 7,500 downpayment assistance on top of the Tax credit!!!
Please contact me to nail details and your needs.