Excellent sound fonts of piano and pipe organ do exist.  Warren
Trachtman is the source for what is generally considered the best piano
sound font.  He has many fine MIDI piano roll scans on his web site:
http://www.trachtman.org/ 

For pipe organ sound fonts go to
http://brucemiles1.mysite.wanadoo-members.co.uk/ 
and for the truly great simulation of a Wurlitzer to play these sound
fonts go to
http://www.virtualorgan.com/RunScript.asp?Page=1&p=ASP\Pg1.asp 

If you are not aware of the MidiTzer you are in for a great surprise!

Of course, a good sound card capable of utilizing these sound fonts
is essential.  The Creative Labs Live! 5.1 sound card can be found on
the eBay stores site, refurbished, for under $20.  I purchased four,
and they all look and perform like new.

John Spradley in Sylmar, California