how to...

[Zillo7]

how do i add a gas station to a pre-existing airport? this airport (ORT4) came with the game so i don't know where to find it.

[sruddy]

Try using Airport Design Editor or FsX Planner (I can't remember if this will make a gas station but should).

[Zillo7]

all i have is fsx planner and it won't compile!

[sruddy]

I have been using ADE much more over the last few months as it has much more recent release.
You could try the support forum for fsx planner here:
http://fsdeveloper.com/forum/forumdisplay.php?f=83
I suggest posting some of the code you are having trouble with in the fsx planner section.

I see some posts in there about fuel stations so it should be possible.

Generally you do not edit the source files in the scenery directory. You can get most things accomplished by setting delete flags in your add-on scenery and then adding in your custom changes.