Hi Sherobot

I'm afraid there isn't (AFAIK). 2 ways I would consider approaching this:

Bring the slides in then select the pics -> picture tools -> format -> click
the little square with arrow thing under size section -> untick 'lock aspect
ratio' and click 'reset'. If you have access to 2003 you could record a
macro to do this - unfortunately you can't record macros in 2007.

Create your widescreen presentation then use the photo album feature to
bring the picture in from the original source. 2007 brings in the actual
pictures (unlike 2003 which used to make them fill for autoshapes which was
a royal pita).

Which approach I would use very much depends on the presentation & contents
but hopefully I've given you a starting point.

Lucy
PS To make sure the presentation is set to truelly fill the screen see here:
http://www.playsforcertain.com/calculate.htm