Netscape 3.0 is accompanied by an audio player that can read ULAW (au), WAV (wav) and AIFF (aif) sound files. A popular MIDI file player is Crescendo by Live Update.
If you have are unable to obtain Netscape 3.0 or additional Plug Ins, it is possible to configure 'helper applications' to play sounds and music that Netscape can't handle. This option exists in the General Preferences menu in Netscape, and works by assigning particular file types to external applications. For example, if you had a sound player you could assign it to play all WAV, AU and AIFF files.
Here are some sound resources on the Web that you may like to check out.
This is a good place to find some really tragic MIDI music.
This site contains quite a few music, movie and television sound clips.
These sounds are in WAV format and are suitable for use with Web pages. Most files are reasonably small.
A huge collection of MIDI music files that have been categorised and archived. They have to be downloaded and decompressed before use.
A small collection of MIDI files that manage to cater to all tastes, from X-Files to Phantom of the Opera.