I don't think you can do this... would love to know if you can... I do have a
work around though...

which is to fake it and import whatever it is you desire to see through the
flash into the background of the actual flash video and use the video to
display both elements. I do this often with objects I need on a powerpoint
page that have more animation needs than powerpoint can supply.

Hope this helps!
Brian

You should set up your slides to any ratio before you create contents. If you
change from standard to other ratio after you have content on your slides,
many objects like texts and images will be stretched wider and distort their
appearance.

See also:
http://www.sameshow.com/forum/viewtopic.php?p=4097#4097

My article about running Flash in PowerPoint may help you step by step:
http://www.sameshow.com/other/insert-flash-into-powerpoint-2007.html

But setting Flash as background in transparent look is not applicable, I
think.

I don't believe that is possible.  In order to play flash content you must
use the player's activex control and that can't be transparent.

Austin Myers
MS PowerPoint MVP Team

Provider of PFCPro, PFCMedia and PFCExpress
www.playsforcertain.com