I came across this a few days ago on Lifehacker.
"Windows/Mac/Linux: With pictures, videos, and high-resolution fonts, slideshows can make up some pretty big files—fine if you've got a large enough thumb drive or CD-R, but what if you have to email them? Sun Presentation Manager, a free extension for OpenOffice, shrinks down files by compressing graphics, deleting hidden slides, and creating static versions of linked objects. It works similar to the PowerPoint-based PPTminimizer, but without the $40 fee and exclusive Office platform—you can use the extension on either OpenOffice files or imported PowerPoint projects. Sun Presentation Manager is a free download, and requires OpenOffice 2.3 or StarOffice 8 or later."