Is anamorphic widescreen possible in iMovie 09?

Yes.

It sounds like you want to do "letterboxing". To do this, try the following:
1. Click on the project you are working on.
2. Select File->Project Properties.
3. Set the Aspect Ratio to "Standard (4:3)" and click "OK".
4. Click "Edit Project" (if you aren't already in that mode).
5. Hover the mouse close to the beginning of the first clip you have in your project, and you will see a sprocket wheel button with a down-arrow on it. Click on that button.
6. Select "Cropping & Rotation".
7. On the preview pane toward the upper left, there are two buttons: "Fit" and "Crop", and "Crop" is probably already selected. Click on "Fit", and click "Done".

Voila!

You may have to repeat Steps 5 through 7 for as many clips as you have in your project.

This feature is not very well documented in the help. The help talks about how to do this when adding NEW video to the project, but if you've already added video to the project and want to switch it, I couldn't find anything that explains it. Perhaps Apple will want to address this? Or perhaps it is explained somewhere that I couldn't find?

Jerman: Just FYI the term "Anamorphic" refers to a process by which filmmakers overcame the limits of the actual width of a frame of film by using a special lens that shot a wider image but squeezed it during filming and then un-squeezed it during projection. This is different than aspect ratios which is what you were really asking about. Most films these days are shot in 1: 1.85 (or Cinemascope which is 1:2.35) and then adjusted to fit 16x9 televisions which are closer to 1:1.78.

I'm actually trying to achieve the opposite to this! In iMovie HD (6.0.3) it was easily possible to capture anamorphic 16:9 into a DV ( not widescreen) project where, provided the option to 'automatically letterbox/pillarbox' was disabled, the pseudo 16:9 footage would retain it's 'vertically stretched' look. The advantage of this is that it was possible to capture a miniDV tape containing a mixture of 4:3 and 16:9 clips, automatically broken down into separate clips (again, via the appropriate preference option) which essentially was an exact replica of what was stored on the tape, in exactly the same resolution, that is, without letterboxing.

However, in iMovie 09, neither the 'crop' nor 'fit' options appear to allow this. Regardless of what permutations I select, the end result is 'corrected' which for my purposes, it actually incorrect!

Anyone have any ideas about this?

Thanks.