With the talk of editing the huge flat map, I decided to try the Source SDK myself. I was met with nothing but problems. My first problem came about when I tried starting it. I clicked launch, it said it was loading..... and then nothing. Eventually, having clicked on the f***ing icon for the fiftieth f***ing time, it finally started. I know for one thing that starting the SDK shouldn't be harder than nailing jelly to a tree. Or eating Gold. Then I was met by another problem in the form of "No game configuration to run with". If anyone has any suggestions that might help, please reply. And no comments insulting my intelligence if it's something obvious.
Eh..hm.. I don't quite remember how to set up the game configurations, but I believe this should help you out there. I used to play with hammer alot, and I like to think that I got quite good with it ^-^ Dunno why you had such a hard time stariting it up though o.o Edit: I'm having the same start up problem too! I just didn't realize because I haven't attempted to use SDK in many months o.o Anyways, that website I sent you will only help you set up the configuration for gmod9, which is pretty much pointless unless you plan on working with a game mode, try looking around on the valve wiki, there should be something there.
Nothing is supposed to be as easy when it comes to this sort of thing, it's supposed to discourage you from making crap if you can't figure it out.
Okay, so since the orange box, sdk's default game configurations are set to those of the orange box (ep2, portal, and team fortress). For those of us that don't have it, what you need to do to get SDK is add "-engine ep1" to the launch options. Once I did that, SDK started on the first time I clicked it, and I had game configurations and what not :D