> This is a dumb question, no doubt, but is there any way to "improve" the quality
> of MIDI instruments? They always sound so fake and computery. Is there a way to
> make them sound more like real violins, timpani, pianos, etc.?

Replace the original samples. This varies on your sound card. With Live and Audigy cards you can load up SoundFonts.

Other than that, you just need a high quality MIDI that tries to reproduce the reverb and other effects in the right places.