Yup installed for me no problem on my glfusion testbed.
I left the directory structure in the correct hierarchy
plugins/newsletter goes into your private/plugins/newsletter
it should be self explanitory.
then head to admin->plugins and install.
One thing, to get the user menu option to work, $_CONF needs to be declared global in plugin_getuseroption_newsletter. Otherwise, it won't work on GL/glFusion sites not installed in the web root.
hmm...is that the $_conf in the private folder? Thanks Lee!