Half exposure? Do you do that with digital or just do a funky blend mode?
There are essentially two methods. I suggest you look it up here at http://www.andregallant.com/new_galleries/...s/montages.html
And for many wonderful examples look here: http://www.stephenpatterson.com/
1) take two images, one everexposed abt 1/3 to 1/2, in focus and at desired aperture. Second exposure taken 1/2-2/3 overexposed and OUT-OF-FOCUS at largest aperture available, like 5.6-1.8. Bracket and practice as there is no sure way to see how the blend will work. Then take two images and blend or overlay. Watch the magic appear. This method creates a more painterly and subtle result and comes from the slide film era and is still used today.
2) In any PP program, take image and duplicate a layer (try on light images with as little black as possible) Leave first layer alone. On second layer, apply gausian blur to taste, abt 10-20 % and then blend, overlay, or use multiply feature. Watch the magic appear. On both layers, adjust levels to taste.
Finally, a word of advice: this can easily be overdone and look gimmicky, so select images that will work and are inkeeping with the statement you want to make with your photographs.