I'm not a SketchUp user so I can't really offer any advice there, but for the render preview you'll need an external renderer. AC3D comes pre-configured to use PovRAY (hit F7 for the render menu) which you can download here:
http://www.povray.org/download/
Here is a list of other free stand-alone renderers:
http://www.independentdeveloper.com/...rendering_soft