Yes, the system is fine. Like maxwh2o says, you would be better off with a 'true' quad core for gaming as well as 3D work. Personally, and I'm sure I will get some flack, the Zambezi isn't quite ready for prime time yet. You'll be better off with the Phenom II X4. But AMD is going to try again with Piledriver this fall (hopefully).
I agree, Phenom II>FX-4100. HOWEVER, if you can go with the FX-8120, its actually very reasonally priced currently. One other critique I would give on your build, is that it would be a good idea to spend a few extra bucks on a 6870 over the 6850, but both are fine.
I'd also consider getting a case without a power supply and a separate one.. More often than not the power supplies that come with cases are garbage.
BTW clutch, Tom's has a first peek at Piledriver with early Trinity Benchmarks, Piledriver is definitely showing promise.