This tutorial will explain the steps to exporting to an AVI file. If you are creating a power point presentation that could be used on a PC the safest thing you could do is export for a AVI file, if you are strickly staying on a mac then a quicktime file is fine.
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 Expert Settings.

3) Next you can click the share button at the bottom and you will be prompted with an expert save screen. First use the drop down arrow beside the word "Export" and choose "Movie to AVI"

4) Now move further down and choose the drop down arrow beside the word "Use" and choose "Animation".

5) Now double check your settings and save your file.
