I don't think this will work with versions of WordPress earlier than 2.8, when the current option pages were implemented. You may want to directly hack the timeout values in the source code if you're running an earlier version of WordPress.
Unpack the zip file and upload the files to
or my favorite,
cd wp-content/plugins svn co http://plugins.svn.wordpress.org/configure-login-timeout/trunk configure-login-timeout