As iMovie, the movie editing app for iPad 2, makes use of front facing camera it is not allowed to be installed on iPad 1. This is restriction from apple you will get the same error message when you try to purchase it from App Store from iPad. However Download Squad, 9to5Mac and few more has got it working but it never worked for me.
The error message which I get when installing iMovie on first generation iPad is Could not install application on device. Error: kAMDReceiveMessageError using the technique suggested.
Also it seems there are Authorization Issues coming up when you sync your iPad with iTunes after installing iMovie this way.Seems like one way or the other,having an iMovie on iPad one will be an iDream for many of us.