When it comes to gas I highly recommend calling in a professional plumber that works with gas due to the potential for explosions, leaks, etc.
Gas is something you don't want to make any mistakes with.
I second Dan's motion. It's too dangerous to mess with if you're not a pro.
Sandy as Dan said and Steve seconded. the gas pipe part can be difficult if not done right and down right dangerous as well. But there is even more to think about when tapping into a gas line.
Many people are doing this type of project on their own and doing it quite successfully or so they thought. When gas pipe is installed in a home the building contractor uses the smallest pipe size they can to do the job. When someone comes along and taps into the pipe system to install a fireplace, or BBQ grill they do not realize that they are causing the gas supply to be undersized if several appliances are running at the same time. Much like an extension cord that must be larger the longer the run or because of a bigger current draw; so must the main gas line servicing the new appliance being connected. We see this issue all the time when we go to a home that has a high efficiency hot water heater installed. The complaint is often that they are running out of hot water, yet never had that issue before. Once we size the pipes for the new BBQ addition we often find that the pipe is not big enough to properly deliver enough fuel to properly operate everything at the same time. Plus you need to check the size of the gas meter as well. They are sized by the gas company based on current demand. When a larger demand is applied to them, they can start reading wrong which can end up costing you more on your energy bill.
The last thing is the flue pipe. With the higher efficiency systems, and depending upon what you purchase, you may need to line your flue to a smaller size so you get the proper drafting needed.
You definitely need a certified gas fitter to ensure that it gets installed according to code and that your insurance carrier will recognize.