Try the FPSC demo, you should be able to find it pretty easily here. It's £40 or around about that, and is easy to use.
I'm not saying that you will be able to make AAA games with it, it's something to impress your buddies, have some fun with, and hopefully expand on. Like there's a few avenues from FPSC to look into, mainly Modelling and Coding - the engine source code is supplied, and loading a level in DBPro is very straightforward, so it is a really good learning step, and you can make a FPS game over a weekend, not too shabby. FPSC would teach you a great deal about game design and how engines work.
TGC releasing the engine source code is kinda like Fisher Price making a 'My First Alarm Clock', then giving it functions to control the fabric of time itself
. There's not a lot of people doing much with the engine code it has to be said, Ryker9 is the only major project - but I think that things will improve for FPSC users before too long, TGC's kinda busy right now and FPSC won't get a look in till things calm down.
As I said, grab the demo and have a play.
Van-B
Aegrescit medendo