Either
Unpack the zip file and upload the files to wp-content/plugins/wp-syntax-hacktify,
or my favorite,
cd wp-content/plugins
svn co http://svn.wp-plugins.org/wp-syntax-hacktify/trunk wp-syntax-hacktify
uglier_syntax_styles.css in your plugins directory (wp-content/plugins)! Use wp-content/plugins/wp-syntax-hacktify/hacktified.css as an example.



