How can I save my PowerPoint 2003 presentation (.ppt file) in Windows so that it can be viewed (including animations) on PowerPoint for Mac?
Your file should be viewable on the Mac without issues, though there are some things you need to avoid. Motion path animations isn't a feature that exists on the Mac version, but it will play those animations in files created on windows. You just won't be able to edit that animation on the Mac.

You should also avoid embedding linked content and anything windows specific, such as WMV video. If you need to link to content, it may work if you put the file in the same directory before embedding, and then send both files to the recipient. 

There is a lot of platform compatibility links, such as http://office.microsoft.com/en-us/powerpoint-help/cross-platform-powerpoint-compatibility-HA010287268.aspx and http://www.pptfaq.com/FAQ00281_PC_to_Mac_and_Back.htm