Help/advice for finishing black walnut slab

I picked up a black walnut slab to make an end-mounted cantilever computer desk out of (the middle piece): [slab](http://i.imgur.com/Q8dn2u7.jpg)

It's dry, rough sanded and planed, it just needs a little finish sanding and coating.

Anyone have any tips on finishing it? What I'd like it to look like when done is essentially this, color-wise: [Ideal result](http://i.imgur.com/5TF3lbW.jpg)

Is that difficult to achieve? I only have a little experience with stain/brush-on poly. I'd like it to have a reasonably tough, preferably waterproof topcoat. I'm also considering trying to keep the bark on one edge, I know as a first slab project this may be unwise but I really like the cut edge of the bark.

Thanks in advance!