Here's what I did: (and again, Sir Maximus, thanks for the handy 8-step tutorial on isolating lines)
1) Lasso or otherwise select the large areas you don't want, like the flowers and much of the background; go to edit>clear
PS: you need to have a transparent BG for this to work well. It's also good so you can put any BG with it or superimpose it on any other image you like. If you need tips on that, let us know.
2) Go to image>adjust>levels
3) Bring the rightmost, white slider, over till teh image goes very bright and white
4) bring the leftmost, black slider, right till it meets up to the white one. Now you will see the black stand out and the middle grey tones will be gone
5) control/command click on the rgb channel (if this pallette is not open, go to windows>channels and open it)
6) this will make a selection; go to selcet>inverse; make a new layer and fill in the selection
6a) you could also use the selection you laready made and go to edit>clear. Try it both ways to see which one works best
7) deselect and get rid of the marching ants
8) you should probably zoom in and check your edges and clean them up, depending on how precise an outline you need
Obviously this jpeg I uploaded needs more work. I could have made a cleaner selection on his shoulder and shirt area, but you can be more precise. You'll have to make a selection and fill in black where it's missing or paint it in. And I would zoom in and use the eraser. if you wanted Otherwise, it should be OK.
Let me know if this helps . . . or doesn't!
Cheers, Clare