It's in ROM/Flash. It's not a real file in the filesystem, so you can't
really rename it. You haven't told us what device or what version of the
operating system, etc., we're talking about. If it's WM5, you might try
creating a little EXE, naming it the same as the explorer program and
copying it over the top of the original in the \Windows folder. The only
way to get the real IE back after that should be a hard reset.
Paul T.