I'm just going to answer just a couple of these questions because I only have a few minutes. I'll try to get to the rest of them a little later.
Anyway, the first file you mention "poster1.zip" is already a g-code file which means that the tool paths have already been generated, so you don't have to convert it to anything. I did notice that it is saved as a .txt, so, depending on which machine controller you use (EMC2, Mach3, Turbo CNC etc.) you may have to rename it so that it has a .nc extension instead.
Search Google to learn how to turn on file extensions for your computer so that you can change them easier. When they are off, you can't see them and, therefore, can't easily rename them. This is a good tip for CNCists as well as just computer enthusiasts in general.
I'm assuming that you meant .ngc and not fgc because I've never heard of fgc, but I could be wrong.
.ngc is really just a g-code file. They have different names for g-code files, for example .ngc, .nc, .cnc, and many more. .ngc is the file extension which I've seen used with EMC2, but other machine controllers use it too probably.
By the way, what do you mean by "depth" when you refer to the jaguar. That file doesn't have its depth set yet. Are you asking how to re-size it so that it is smaller?