Technique query - 2 photos to one photo
Best use Cs5. I use a PC. Usualy I do this:
Open both images. Now decide what is your main image. Go to second image. choose lasso tool and lasso person you want completely, does not have to be deadly accurate as extraneous will be masked away later) , ctrl c the lasso on a PC.
Open main image ctrl v, then v and move lasso to where you want it.
A new layer has been made with the lasso click on this layer and click on mask icon. If the image is too big or too small use the transform tool to make bigger, rotate and so on. Click on mask, b (brush) and choose black. Choose brush size with... [key or.... ] key paint away the areas you do not want from the lasso. use x to change from black to white.
If the colors saturation lightness do not look good ( often photos taken at different times, with a different camera and so on) click on lasso layer and choose, for instance the hue saturation transform, or the curves transform.
Brush, transformation and mask technique look for tutorials.
Hope this helps. I say it is what I usualy do but of course I diverge from this system when needed.