That tutorial is based on 'Photoshop Top Secrets' DVD's video tutorials.
It's takes me a lot of time to doing this 
You will learn here how to create something like this:
using these two pictures
You can download sample files from here:
lizard (jpg)
hippo (psd)
As you can see the picture of hippo is saved in psd and it's cropped
(I've uploaded it cropped to save your time and because this is not
our problem here ).
Ok, let's rock!! ^^
1. Open the lizard photo and paste hippo to it.
2. Check hippo layer and use the Free Transform tool
(Edit -> Free Transform or CTRL+T / COMMAND+T)
to get something like this:
TIP: Hold SHIFT button to scale your picture proportional.
You can rotate your image by riding your mouse near
the corner of the Free Transform tool frame or use
Edit -> Transform -> Rotate
3. Let's colorize your hippo head now:
a) make sure that you have hippo layer selected
b) hold ALT button (OPTION in MAC) and press the black and white
button 
placed at the bottom of Layers window and click
'Color Balance'.
c) in new window check 'Use Previous Layer to Create Clipping Mask'
and click OK
d) now you will see the 'Color Balance' window. In Midtones type
these numbers: 0 +40 -100
e) change to Highlights and wrote this: 0 +29 0
You should see something like this now:
4. Check your hippo layer and click 'Add vector mask' button 
placed
at the bottom of Layers window
5. Make sure that you have default colors set (press D to do that),
You should have set Black color on foreground.
6. Take Brush Tool (B) and mask areas showed below
TIP: Don't afraid if You masked too much. Just choose the white color
as your foreground (if you have default colors just press X to change
between foreground and background colors) and unmask area that you want 
You should have similar picture to this:
7. Let's do something with parts of lizards' head now
a) check lizard layer
b) Pick up Clone Stamp Tool (S) choose big (about 200px) and smooth brush.
Hold Alt/Option key and click here:
TIP: Doing this you have selected an area to clone
c) stop holding Alt/Option key and click on lizards' nose a couple of time
until you have this:
d) change brush size to about 60px and target (with Alt/Option key) that area:
e) now clone that to the white area
You should have that:
8. Click the top layer and make new layer. Call it 'skin'
9. Check Clone Stamp Tool and make sure that you have selected 'All layers'
in the top bar
10. Now we will clone some lizard skin. Free your mind and spend some time to
work at it. This is my result:
That could be over but we will work with some lighting effects
Going to try this one with your images and also with own images if I find some time. 
I have got it in my mind to try this tutorial, but I didn't found any time yet. 
maybe my father with a cow 
