This method with these files works flawlessly on my Macbook Pro 2.66 gHz i7 running OS X 10.6.7

Step 1: 
Extract the .rar file

Step 2: 
Open the "Myst IV Revelation" Installer

Step 3:
Double-click the .iso file in the "DVD 1" folder to mount "Myst IV DVD 1" and click continue on the installer

Step 4:
When the installer asks you to "Insert Myst IV DVD", simply double-click the .iso file in the "DVD 2" folder to mount it to your desktop and click continue for the installer to finish.

Step 5:
ENJOY!!! Your "Myst IV Revelation" application bundle is located wherever you opted to install in on your computer. Drag it wherever you please, or leave it there, your choice.