TiMIDIty
The easiest pversion to work with, is here
h**p://www.stardate.bc.ca/eawpatches/html/default.htm
For ease of use, the Win32 version, but for BEST QUALITY, the **Slower, but still realtime plus on >300MHz CPU** C-Spline commandline version, plus the GUI addon to assist you.
You will also need the patch set from the same site, or to look for alternate instrument sets if you prefer - It uses Gravis Ultrasound compatible patch sets - and a full, good quality set is QUITE LARGE.
SEE Also - the "EASY INSTALLER"
h**p://www.stardate.bc.ca/eawpatches/html/easy_install.htm
Another patch set
h**p://www.anime.net/~goemon/timidity/
This is a TGZ (unix) format kit, but should be ok with the windows version.
Look for "GUS patches" and you may find others, but the set with Timidity is a pretty well worked combination.
MidiNight Express is another possibility, or would be if it wasn't CRIPPLED - unless you buy the CD, the sound set is minimal and only fully supports the demo tunes.
Your other possibility is to "loopback record" while playing through the soundcard - many can do this without a link cable if you choose "Stereo Mix" or equivalent as the recording source.
The quality then depends on the soundcard, from a good Hardware or software wavetable, down to the Microsoft Synth on any WDM-driver soundcard, with "FM Synth" not really worth trying.
