The problem with this is that when Eclipse doesn't know what to do
with a given file, it opens it with the so called "System Editor",
which actually is... whatever your OS says it is, hence the "rolling
dice effect". I don't think you can tell the OS to use Eclipse as the
default editor (though I didn't try; anyway I wonder why anyone would
actually want to do it), so you have two alternatives: either install
an eclipse plug-in to manage the kind of file you want to edit (like
e.g. pyDev for python), or go to Window > Preferences > Editors >
File Associations and associate your file extensions to the built-in
text editor in Eclipse.
I happen to be a heavy user of Vim, Emacs and Eclipse, and for
this job Emacs is definitely not what you really want, though if
you want to try it for its own merits, Emacs can substitute Vim quite
well (modal interface and all), look for viper and vimpulse.
FYI: I came here after reading your post