keyframe the alpha values of your materials
i'm assuming oyu know where the transparency is for the materials and that by right clicking you can bring up the context menu which has an option to keyframe it
that's a "Ch" pronounced as a "K"
Computer skills I should have:
Objective C, C#, Java, MEL. Python, C++, XML, JavaScript, XSLT, HTML, SQL, CSS, FXScript, Clips, SOAR, ActionScript, OpenGL, DirectX
Maya, XSI, Photoshop, AfterEffects, Motion, Illustrator, Flash, Swift3D