Faster shutter speed will "freeze" the subject, but you what you get in shutter speed, you give back in terms of "depth of field" which is the zone of reasonably sharp focus you have to work with.

The ISO 400 film will help you use a slower shutter speed with a smaller lens apeture opening, which increases the depth of field. Think of it this way, when you squint and make your eyes "smaller" you can focus on more things closer and farther away from you, whereas the wider you open your eyes, the thinner the zone of focus gets.

As a fun exercise, try a few shots like this: get someone else to drive your car at a moderate speed past where you're standing. Select a slow shutter speed and track the car with the camera like a movie camera would while snapping the shutter. Try to be steady with the "pan" and the result should look like your car has been turbocharged, the car will be sharply in focus, but the background will be whizzing by. Have fun!