The new natural gas fireplace insert will be operating fine than all of a sudden poof it goes out and sometimes the pilot will go out when it shuts off the fire. It was proffesionally installed by the dealer including the double pipe installed in my chimmney flue for intake and outake. The dealer and gas company have checked everything and they say everything is ok.I also have a gas furnace and hot water heater and they have no problems, need some help as nobody wants to admit that there is a problem.

Have you checked to make sure the pilot isn't clogged with junk. You can take a can of air and blow it in the pilot whole........ http://www.madisonfireplace-patio.com/FAQs.htm
go to this website... this is where I use to sell gas logs... if you have a hard time understanding it call them.. they can explain... very smart people

what modifications need to be done to replace a gas insert fireplace with a wood burning stove?

The entire venting/chimney needs to be replaced. this is the most crucial part. gas appliances use "C" and "B" venting materials, which are single walled tin, and double walled tin respectively. these are not sufficient for combustible solids.

Burning solids requires an "A" vent. this is similar to a B vent but (it's been 10 years since i read this) it has a layer of insulation inbetween the pipe walls to keep the heat inside the chimney, and are much more air tight.

Call a professional wood burning stove installer, and they will do it PROPERLY. "A" vent is VERY expensive, (you could spend as much on the venting as you do on the stove) and you don't want to make any mistakes, or do it incorrectly.

removal of all of the other venting materials should be done before they get there to reduce cost.