Even though I'm a do-it-yourself proponent, converting a wood-burning fireplace to natural gas is definitely one project you DON'T want to do yourself! Improperly installed, gas piping can have explosive consequences.
Secondly, if you want to install a gas burner into a formerly wood-burning fireplace, I hope that you are independently wealthy. These burners are huge energy-wasters, and some burn as much gas as the furnace or boiler that heats you entire house. They also pose a large risk of carbon monoxide poisoning, as they do not do a good job of fully combusting the gas. And they produce tons of moisture: gas, after it burns, is 80 percent water vapor and very corrosive to the inside of a chimney.
So, instead of converting your wood-burning fireplace to natural gas, my advice is to stick with the wood-burning fireplace or install a wood stove insert into the brick fireplace, which will increase its efficiency.