I need some help with ideas. The cake is for a lady turning 100 who loves jigsaw puzzles. I want to do a stacked cake and incorporate the 100 too. I'm thinking it'd be neat to make the pieces from fondant and have some missing. Any one have any ideas? TIA!

Patchwork cutters has a jigsaw cutter / mat. Here I found a example /even with cake/ http://www.flickr.com/photos/creativecake/3767446629/in/set-72157621755409471/

Could be a nice idea to expand for stacked cake.

I know this is just a sheet cake; but this was done all in BC. Maybe it will give you an idea. It sounds like a lot of work in fondant.
http://cakecentral.com/modules.php?name=gallery&file=displayimage&pid=53646