http://www.antistatic.org/winmdcd/
From the author's site:
"WinMDCD is a Windows MDC-1200 Decoder. ... The decoder will decode all single-packet op codes and arguments. Descriptions for known op/arg combinations are built in. ... This software uses the sound card input from the headphone jack of the scanner."
Doesn't require an installer. I believe it might write to the registry but I'm not sure.