How do I build a video from slides from a keynote presentation recorded audio?

This should be pretty easy.

First, assuming your export from Keynote went OK, you should have a series of PNGs or JPEGs to use.

You should also have your voice recording available. If possible, your voice recording should be in AIFF format for best results. You can do this conversion in iTunes if necessary. Let me know if you need instructions.

It is generally a good idea to put the voice recording in iTunes before using it in iMovie, although you can also just drag in the file from the Finder. The danger of dragging it in from the Finder is that it is easy for you to move it somewhere else later, and when you do, it will break the link to the file in the iMovie Project.

Also, you can make thinks easier by putting your PNG files in iPhoto and creating an Album that contains these files, in order. Aperture works as well if you don't use iPhoto.

OK now for the iMovie part.

First, start a new project. Also, click iMovie/Preferences and make sure the Advanced Tools are enabled.

Drag your Audio track into the empty project.

You should see a small gear icon at the top left of your audio track. Click it, and select "Clip Trimmer".

Now, play your audio in the Clip Trimmer. At every point you would like to change the Keynote slide (except the first slide), type M to add a Beat Marker. When finished, close the clip trimmer.

Now add your photos. If they are in order and in an iPhoto album, you can open the Photo Browser in iMovie and navigate to the Album you created. You can drag the icon for this album into the iMovie Project. The photos will be added at the Beat Markers. Alternatively, if you have not created an album, you can add the photos one at a time and they will snap to the beat markers.

Then SHARE your movie in the sizes that you want, and you are done.

Here is a link with more on Beat Markers. http://www.kenstone.net/fcp_homepage/imovie_09_stone.html#markers

You could also do this manually, without beat markers, by adding the slides, adding the soundtrack, and manually adjusting the duration of each slide. I just think the Beat Markers way is easier.

Let me know if you have any questions.

Sure, you can do it manually.

The thing to remember is that iMovie is a video centric, not audio centric. So with the exception of beat markers, you must generally have video on your project or the audio will truncate to be the same length as the video.

In your case, you could overcome this by going to File/Project Preferences and setting the default length for new photos that are added to the project. Set the length to a number that when multiplied by your number of slides will cover the length of your audio. Then you can fine tune the duration of each slide by opening the clip inspector and setting the duration.