Does the shn file type appear at File > Add/rescan > File types? If so, did you check it?

I have MM 4 and I downloaded in_shn.dll to the plugin folder in MM. I restarted the program but the files are not showing up. I want to know if I'm doing something wrong; I downloaded the plugin from this location: http://etree.org/shnamp.html

Is there something else I need to do?