Mining with GPU's is almost extinct now. Because of the exponential growth in difficulty, currently 11,187,257, a single 7970 will only earn 0.02922023 every 24 hours.
Given that the difficulty is set to jump massively due to the upcoming flood of asic hardware, you should invest in other ways in order to make your bitcoins back.
I'd suggest investigating AMC shares and ASICMINER shares and/or purchasing asic harware, though delivery dates aren't always honoured!
Good luck.