Export from iStopMotion Pro to edit in iMovie 09

I'd like to export a time-lapse movie I created in iStopMotion Pro (I started from very high quality JPG's, shot with a Nikon D700), so I can edit it in iMovie 09. Apparantly, iMovie does not import .mov files, so I tried "DV-PAL 16-9". Now, I don't know where exactly things change, but the end-result looks bad compared to the original movie I created in iStopMotion.
While I'm working in iMovie, the quality I see there, is already low, but maybe this is normal while working as you only see some kind of low quality preview? I'm not sure about this... But, in the end, when I save the iMovie result as HD 1280x720 (using the highest quality preset with 'Export Movie'), it doesn't improve. The quality remains low. To be more precise: the movie is less sharp and straight lines get this ugly jagged look.
What am I doing wrong here?


Thanks a lot for that Steve,
I have an NVIDIA GeForce 8600M GT 256MB graphics card with 4GB RAM so is this considered slow? what would be the minimum for smooth playback of full size video. Is there much loss in quality when it's downsized? What other video editing software would you recommend. I'd like to burn projects to DVD with minimal loss in quality and know that exports to iDVD compress the video where you get considerable loss.