James Symington , Oct 19, 2009; 07:11 a.m.
It is going to be 2 things in my opinion. Getting the lighting just right is one of them but probably even more important in this context is your sharpening strategy. Just getting it done in-camera will not be good enough to get to the level of the link you posted. You will need to do capture sharpening just to pep up the file, you will need to selectively sharpen parts of the image (often the eyes only) and then you will need to sharpen again to output it ot screen or print etc. The sharpening issue is a surprisingly vast and knotty one and you will need to read and practise much. A good start is to read postings by a chap called Patrick Lavoie on photo.net. He can be blunt but he does this kind of thing for a living and what he says is spot on.
It's not your lens - at f8 it will sing provided you have exact focus on your subject's eyes which it does not appear to be on your Facebook link. Also at f8 you may have too much depth-of-field to get a really good 3D effect going - try f4 for example or perhaps wider even.
Here's a very casual shot taken in natural light of my little daughter yesterday. Handheld on a D700 with the 50mm f1.4 G at f1.8 I think. Focused on her left eye and the only part of the image I sharpened were the catchlights on her eyes from the window.