What I meant, does the help or even the manual (which should) say how to change the aspect ratio of the preview monitor (I don't know how iMovie calls it, the window where the video is being played back)? I don't have iMovie HD, so I can't look there.
As you have videos that have the resolution of 544 x 304 and 537 x 300, the proper aspect ratio for those is 1.79 (calculated via 544/304 and 537/300).
1.79 comes very close to 16:9 (16/9 = 1.7777), which is called widescreen.
Fullscreen is 4:3 which is 1.3333 (4/3).
from http://en.wikipedia.org/wiki/Aspect_ratio_(image)
from http://dharmadevil.com/widescreen/
Do I understand you correct, that you want to make a 4:3 video using the 16:9 footage?
Have a look at iMovie's effects and see if you can scale or stretch the movie.
Again the manual might be of help.
You should also consider a thread title change, as yours is not very descriptive.
To edit your thread title, just click on the
button on the bottom right of your original post and then click the "Go Advanced" button below your message.
Example:
iMovie HD: have 16:9 footage, want to cut 4:3 video. How? or
How to use 16:9 footage in 4:3 aspect ratio in iMovie HD? or
....