qountzero,
If you could click on the image that would be easier, triggers are the way
to go there.
If you want to use mouse over though triggers won't work. The best thing to
do then is to make two slides one with the small image and one with the big
image, then on slide one use an action setting on the image that hyperlinks
to the second slide. On that slide create an invisible object, say a
rectangle with no fill and 99% transparency and put it behind the image,
give it an action setting to hyperlink back to slide one.
See this tutorial from magician Glen Millar, who explains it far better than
I can, using the trick to colour an image.
http://www.pptworkbench.com/html/mouse_over_images.htm
