Bround poly frustration

Hi all,I am new to scenery design, although not to FS or FS design. I am finding scenery design much harder than anything else I have tried before, including building aircraft.I am trying to make an airport scenery for FS2004.What I want to do is to create a high res background for my airport to start with.I have great source imagery but I have no idea how to start.I have read that you can use ground polys to create the tiles to put the ground photo textures on.I have tried using sketchup, Gmax and now Sbuilder but I just do not know how to get started.Can anyone give me a quick step by step on how to do this, I don't care at this stage which of the design tools is used.I want to achieve something like the 1024x1024 photo tiles used by the likes of UK2000, Aerosoft, Fly-Tampa etc as the base for my airport before I start making the buildings and creating the ground polys for custom runways, taxiways, taxi lines etc.I have spent two days looking for this information but have not found anything that takes me right from the very beginning.Thanks in advance for any helpGarry