OK, that is iMovie HD you have. The latest version is 6.0.4, which is what I tested against.
You perform a select-all on the images in your time line. Choose the media tab and the Photos tab for that. That displays a button that says "Show Photo Settings". With the images selected in the time line, click that button to bring up a window to set the frame count and ken burns effect. Tripple click the numbers next to the turtle. The first is seconds and the second is the frame count (0-29).
I'm seeing a bug where you can't create less than 11 frames per image, so it would seem you can't do the .2 seconds (6 frames) you are looking for. I get the Invalid message; "Fell short of minimum. The value must be between 00:03 and 60:00.". My iMovie HD has another problem, so maybe this is only affecting me.
You might want to look into
iStopMotion for this type of work.