You can open and play Motion project files in QuickTime Player by selecting the project, pressing Option-Command, and dragging the Motion file to the QuickTime Player icon in the Dock or Applications folder. Or in QuickTime Player, you can choose File > Open, navigate to a Motion project in the resulting dialog, and click Open.
However, if you are using Motion 1 in Mac OS X 10.4 Tiger, you won't be able to do this. If you want to play your Motion 1 projects in QuickTime Player, you can save the project as a QuickTime movie; just open the project in Motion and choose File > Export, or File > Export using Compressor.
This document will be updated as more information becomes available.