I think that there is some misunderstanding on how USVN works.
If you look at the directory structure of a fresh install, the directory of ./public/login does not exist, it's a 'virtual' directory.
USVN makes use of mod-rewrite, which you do appear to have enabled, but you might not have the apache set up to allow it to function. You also need an alias configured.
As a test (this probably opens things up a bit too much), try these settings in the file that defines the web site.
Assume a vhost with it's docroot as /var/www/site and usvn installed in /var/www/site/usvn
Code:
Alias /usvn /var/www/site/usvn/public
<Directory "/var/www/site/usvn/public">
AllowOverride All
</Directory>
Also check your error log and see if anything is showing up in there