As mentioned above by tihs1313 you can achieve this effect rather simply using most any video editor by utilization of the green screen effect.
I did this without much difficulty during the CT5 beta testing phase: http://www.walmarko.com/TheWall.wmv
Unfortunately, this was created before I had viewed the CT5 tutorials, and gained better knowledge of the abilities of CT5 which is quite powerful once you spend a little time learning the latest capabilities. Nonetheless, the green screen/chroma key function would need to be applied regardless.
I used Magix video editor for the clip which is very simplistic in performing green screen.
Hope this helps,

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