I can usually find any answer I need on this website, so I'm a bit embarrassed to be posting on such a common issue, but I'm stuck...
Please have a look at this video to see my problem (which you can see even with YouTube's compression):
The images I have in this scene are illustrator files, and I've tried everything I can think of to get rid of the aliasing: motion blur applied, continuous rasterise on/off, create shapes from vector layers, using the ray-trace renderer with high quality and cubic anti-aliasing filter. Still experiencing unacceptable results.
I'd like to lower the opacity of the images to create a more natural blend with the scene, but my client is adamant that the logos must be opaque and stand out.