Well Premiere sucks for doing such effects.
While trying to reproduce these effects I was basically pulling my hair out screaming at the stupid Premiere programmers.
The effect that is closest to this is the Clip effect. Clip does not support Alpha channels though. So you can't use a Alpha transperancy with it. You can specify a Fill Color, and then use a Chroma Key to get rid of the color to show the background. To move it though, I would have used Transform, but Transform only supports Alpha and not a Fill Color. So the two will not work together.
What will work is a combo of Motion + Clip.
Setup clip with a fill color of Red:0 Green:255 Blue:0 <---pure green.
Then adjust the sliders so that it chops away the edges of stuff you want to get rid of. The piece that you want to show through should be surrounded by bright green.
Then go up to transperancy and set the Key to 'Chroma'. Then select the bright green from the little thumbnail and set the 'Similarity' slider all the way to %100. Hit okay.
Now you should have whatever clips you want in the background showing through, or a black background if you don't have any other tracks below that one.
Next you can goto Motion Settings, then set the fill color to the same as Clip's(pure green) and add your motion.
You can keyframe(look it up in the manual), to adjust what portion of the video is showing at a certain time.
NOW!
The only problem with this is that if you look at the edges of the clips you're adding these effects to, you _MAY_ notice a little green flicker around the edges of it, which really sucks quite bad. I have not really figured out how to get rid of that, but if Premiere's programmers were worth a shit, they would have done a better job, OR ADDED FUCKING ALPHA TO 'CLIP'. There shouldn't be any clips in there that rely soley on FILL COLOR. While we're at it Premire's Transform effect sucks ass to since it has a crappy resize algorithm.
Pheeew...
Okay well, you could also do such a thing, were you pre-process all your clips with the Clip effect, export those, and then import them into your final project and you can use motion or transform using Alpha instead of Chroma key which MAY get rid of the green flicker around the edge. :\
Anyways...
Here is a demo on what all this stuff does. Oh and actually the flicker around the edge looks red since I used Pure Red for this tech-test instead of pure green to see if I could get rid of the flicker. Didn't help much
<a href="http://home.attbi.com/~klinky/flowers-test.avi">Demo Video</a>.
~klinky