My rig is an X2 3800+, bumped to 2.2 ghz, which more than meets the cpus requirements. I haven't upgraded my video card in awhile, though, so I'm using a 6600 GT, slightly less than the "recommended" hardware but well above the minimum requirements.
The game setup utility recommended the "medium" graphics level, so I let it install to the defaults.
So I'm not at maximum resolution and I don't have all the eye-candy elements turned on.
Game still looks great, it flows smoothly without any hiccups and it's been a lot of fun to play.
So, in short, the game will still look incredible if you run it at the medium settings. But if you want to run at the max (1280 x 1024, anti-aliasing on, full shadows, full details, etc.), you probably need to have a cpu running at 2.4 ghz (AMD) or 3.4 for Intel and a $500 - $600 video card (X1900, 7900 GT).
I'm getting by quite fine with a 6600 GT right now, but I'm going to upgrade later this year ... not so much for the resolution, but so I won't be slowed down when I install the mods that other people, more talented than I am, are now working on (better heads, improved bodies, more people added to the game, more monsters and critters, etc.).