To create a preview:
Preview - Grab Viewport
Create Preview Animation. If you are using Enhanced menus, choose Rendering menu
Screen Capture
Create Preview Animation.
If the output type is AVI, 3ds Max renders the preview and saves it in a file called _scene.avi, in the path specified by Configure User Paths
File I/O
Previews. Immediately after rendering the preview, 3ds Max runs the Media Player with this animation loaded.
If you dismiss the Media Player and then want to view the preview again, choose Tools
Grab Viewport
View Animated Sequence File. This restarts the Media Player with _scene.avi.
You can save the preview under a different name, so it won't be overwritten the next time you make a preview. To do so, use Rendering menu
Screen Capture
Save Preview Animation As.