The horizontal line you're talking about is the Color Grid Stabilizing
Wire; removing or altering it in any way would make your monitor much more
fuzzy. Most overhead projectors don't go through the monitor, so the
stabilizing wire shouldn't be a factor. If your projector does go through
the monitor, you may want to replace it with one that connects directly to
a video interface card instead.
Check the Redgate Buyer's Guide library here on AppleLink for possible
sources.