How do I import videomaterial from iMovie so that it keeps its quality (hd) ?

It is not "iMotion", just "Motion". Export as a full resolution Quicktime file. Import that into Motion. Be sure the Motion project is the same specs as the QT clip you're going to import. I.E. do not create an HD 1080 Motion project and use standard def clips. That will blow up the SD clips to fit the much larger 1080 frame size and ruin the SD clip's image quality. Can't blow stuff up too large.

So what format are you editing in iMovie, and what format are you setting up your Motion project for?

There are also Render settings that can effect how clear the video appears in the Canvas. This is not how the video will appear upon export. There is no image loss when you bring a video into Motion or FCP X properly. No quality loss at all.

Motion is not an editing application, and will not let you edit video very well. Wrong tool for the job. FCP X will get you through editing much faster and easier. Motion is for grahics and effects only.