Smaller yes, larger no (without refilming.)
The larger the image on the screen the greater resolution you would need in
the movie to prevent "graining" of the movie. Movies are basically a series
of bit mapped images that are shown very fast (roughly 30 frames per
second). Just like any bit mapped image the larger you make it the more
distorted it becomes.
Also, when you create a movie (mpg or wmv) you are compressing the original
image down even further and may very well be using a "lossy" compression
technique. If this is happening you are actually losing bits that would
support a larger screen.
It is best to get movies from a DV camera as an uncompressed AVI file if
this is possible. Crop and edit your movie and then save it in the proper
format for your project. I have all my raw movies saved as AVI first, edit
them and then the conversion to MPG takes place when placing on DVD or as a
movie (either MPG or WMV) I will show from my computer's hard drive. BTW,
uncompressed AVI files take an enormous amount of hard drive space per
minute of video.
