I ended up talking to Apple for about an hour and a half yesterday on a long distance skype call from New Zealand to USA trying to figure this out.
The day before, an Apple employee in the sales department actually sold me iMovie v9.0 (2011 version) and was very helpful/ confident about it. He knew my operating system limits and knew that Mavericks and the current iMovie v.10.0 would not work on my macbook. Even the order confirmation/ receipt said "iMovie '11 single unit". Sure enough, what he sent me the next day was a download for the current iMovie v.10.0 and of course when i tried the redemption code in the App Store it says it will not work. This is what led to the very very long call.... Long story short, spent an hour alone trying to get the refund sorted out with an absolutely useless employee in the sales dept who said "wow thats really old!" when we went over my operating system details for the zillionth time and who did not know what iMovie 9.0 was. Eventually though, i ended up with the right guy in the Apps department who set me straight. He sent me iLife '11 via disk (to my U.S. address) which includes iMovie 9.0. Voila, it can be done.
What i learned: Previous versions of iLife can only be obtained via disk and not through the App Store, apparently. Same goes with anything that came out pre-App Store. What i read online leads me to believe otherwise, but not with my operating system (Lion).
Hopefully this helps someone in my shoes searching for this very same topic......
Cheers.