Laptop

The result

How to

1. Go to http://www.istockphoto.com/file_closeup.php?id=12766331 and download the full resolution source (HD1080 1920×1080 px @ 30 fps)
2. Download free After Effects project from here
   Note: you should have Adobe After Effects CS4 version (or greater)
3. Unzip the project and open it in After Effects
   
   You can find Camera1 in the scene and Null1 object with animation keys. The keys was imported from the 3d application where the laptop was created. Thus you can put your own 3d objects and they will have a correct perspective. If you want to link an object to the laptop screen just link it to Null1 object. You can also replace the background with your own.
4. Replace the file laptop_comp.mp4 in the project with the file downloaded from iStock. Right-click on the file name in Project window and choose Replace footage>File
   
5. Put your own content to the screen composition.