If you mean save as avi of wmf then no you can't. There are conversion
programs out there, some better than others. If you're buying make sure it
does what you want before parting with cash!
If you just need a simple video of your presentation you can get CamStudio
free and it will record the screen. There are also freetrials of eg Camtasia. http://camstudio.org/
Wondershare PPT to Video can convert PowerPoint presentation to
various video formats such as MPEG-2, MPEG-1, MPEG-4, AVI, WMV,MOV,
3GP, etc.
You may get it at http://www.ppt-to-dvd.com