Somewhere here I have the pictures of the Stand-By Generator i had installed. It runs off Natural gas, and has an Automatic switch to start it up, and transfer the power from the pole to the Generator.
These can be a bit pricey, I spent around $5000 total for the install, and did a lot of the work myself.
I went the propane route, reasoning that gas and diesel will be very much in demand if the deliveries stop. Someone might not wish to barter their last gallon of gasoline, needing it for their car or generator, but will be willing to barter the propane from their grill and cook over a campfire. Propane doesn't go bad.
One thing to think about with natural gas is it's not always available when you most need it. During Katrina, they shut it off to prevent fires. This is likely to be the case with any big event. Perhaps you can drop a tank on the property and get the kit to convert to propane when you need it (@20 minute job)? My neighborhood has propane, so I've got 250 gallons ready to go under my front yard. My stove was set up for natural gas. All I had to do was switch the nozzles and reset the regulator. Call the manufacturer of the generator and ask, or check the owner's manual. They are small and will be taped to some cardboard on the back of the generator or in the manual.