A scripted render effect for 3ds Max.
Once installed and run, you can find the script under Render Effects.
You need to turn on object motion blur for all objects and the camera in Object Properties. Whatever you do, DON'T turn on Object Motion Blur in the render settings.
The images are supposed to be aliased, so don't worry if you've got jaggies everywhere.
You definitely need to render to a 16-bit per colour file format, preferably PNGs, as 8-bit colour isn't good enough.
If you are using After Effects, make sure that it is set up for a 16-bit project.
If the objects in your scene aren't moving too fast, you won't see much difference in the colour of the motion vector images, but it is there, believe me. ReelSmart will find it...
You don't need to render the motion vector images with maps and materials. Just copy your final scene and apply a standard material to everything. It renders much quicker, and the results are the same.
Click here for the script. (2 Kb)
Just put it in your scripts folder (or make a new folder for it) and run it.
If you find any bugs, just send me a mail
As far as I know, this script won't do any damage to you, your computer, or your Max installation, but I can't guarantee anything. If something should go wrong, I'm sorry, but I'm not liable. It's free, after all!