LAME is a well-regarded encoder; I use the Linux version from scripts written by myself, but there is a Windows version as well:
http://lame.sourceforge.net/links.php
You might consider variable bitrate. It might be worth arranging a blind listening test using the same piece of music at 320 and 192.
More info here: http://wiki.hydrogenaud.io/index.php?title=LAME