This tutorial will explain the steps to exporting a CD-Rom sized quick time file from iMovie. Please note that iMovie does NOT burn a cd with your video, all iMovie will do is export your footage to be appropriately sized to fit on a CD-Rom.
1)Once you are done editing your footage in iMovie you can click on File > Export.

2) Now an export screen will pop up, click on the QuickTime icon across the top and then move down to the "Compress Movie For" drop down arrow. Here you will choose CD-Rom.

3) Next you can click the share button at the bottom and you will be prompted with a save screen, choose where to save your file and Type in a name. Now you can save it and burn it to a cd.

(Tip: If you save your file to the desktop and insert a blank CD you can simply drag the Movie file to your cd to burn it.)