It wouldn't be that difficult to use Sapphire Trix or MSI afterburner. Just set your clocks/voltage and save them to a quick load profile.
I good starting point for voltage is 1.094. I had that on my Gigabyte Radeon 7970ghz along with a 1ghz gpu clock and it was stable. It's good to undervolt when your mining because it will help your card last longer and keep it cooler.
Keep in mind that your voltage settings may vary. If it's not stable at 1.094, bump it up to the next step (1.1?) and try again.
Also, I agree with dorsetknob. Your card is probably on the way out. It may help it though if you run lower clocks, less voltage, and cooler. Take the side off your case and put a house fan to blow in it if you have to. I tried to keep my cards below 80 degrees. The cooler the better.