To do so:

in .htaccess in the directory in question:

IndexOptions NameWidth=80

from http://httpd.apache.org/docs/1.3/mod/mod_autoindex.html#indexoptions

Rick has posted a blog on some Big screen http://betterlogic.com/wpr/index.php/2007/08/25/increase-your-screen-realestate/#comment-21 – wow wouldn’t I like to have them!