Hey Grip.
Well, first of all: for HD graphics... you have to make them. There is not setting you amp up like in a videogame(of course). Sure, in the setup.ini of your final build you can elevate the resolution but thats not really going to help, is it?
HD Graphics are in the textures, the shaders and the models you use. (altough this is not directly "graphics" but the way you design your level matters too.)
You best get familiar with the artsoftware you intend to use,for example: Photoshop, and your 3D editing software.
Remember to get FPSC's shader system to know, it has a few different rules than the material systems in most engines.
I dont want to sound disencouraging, but you will likely need a year or two of experience to create HD quality graphics but...really: The path is the destination if you like designing stuff.
Also look at FPSC-HD stuff by EAI and Bond1...learn how their assets are constructed.
Happy development
-Wolf
Check this out about
HD texturing.
Textures are insanely important when it comes to making a game look good. Never neglect them.