Trying to composite from Lightwave 3D using Green Screen

Regards,

I am trying to do a simple picture crawl across the bottom of my video. First I tried using a transparent.png file that was 2240x540 and using the ken burns effect cropped it to move across the screen. This worked to an extent. The only problem is that imovie scaled the resolution to match the horizontal measurement of 960 pixels. leaving the image in a very low resolution. On that looked horrible.

Second try: I own a copy of Lightwave 3D 9.6. I love this program! I figured I could output video that had the crawling photos across the bottom, with green screen as the background. I output it in Apple Intermediate Format for ease of import. and when I place my crawl as a b-role/green-screen the entire image disappears.

Does anyone know what I am doing wrong. I would love to figure this out so that I can composite my 3D animations on top of my imovies. I love the simplicity yet accuracy of the new iMovie 09. I just want to figure this out.

Any help would be appreciated.