Tweet this page

Same idea as my "Tweet this topic" and "Tweet this post" snippets.

I realise that some web hosts may block the use of file_get_contents, but there are many workarounds available.
A quick Google search for an alternative to file_get_contents should do the trick

#
#-----[ OPEN ]------------------------------------------
#
includes/functions.php
#
#-----[ FIND ]------------------------------------------
#

    /**
    * Generate page header
    */ 

#
#-----[ AFTER ADD ]------------------------------------------
#

    /**
    * Put in a long URL, get a short one back out
    * http://www.scripting.com/stories/2007/06/27/tinyurlHasAnApi.html
    * http://fyneworks.blogspot.com/2008/08/tiny-url-api.html
    */
    function TinyURL($u)
    {
        return file_get_contents('http://tinyurl.com/api-create.php?url=' . urlencode($u));
    }

#
#-----[ FIND ]------------------------------------------
#

            'ROOT_PATH'            => $phpbb_root_path, 

#
#-----[ AFTER ADD ]------------------------------------------
#

            'TWEET_PAGE'            => urlencode('Check out this page: ') . TinyURL(generate_board_url() . $_SERVER['REQUEST_URI']), 

#
#-----[ OPEN ]------------------------------------------
#
language/en/common.php
#
#-----[ FIND ]------------------------------------------
#

       'TRACKED_PHP_ERROR'   => 'Tracked PHP errors: %s',

#
#-----[ AFTER ADD ]------------------------------------------
#

       'TWEET_PAGE'         => 'Tweet this page',

#
#-----[ OPEN ]------------------------------------------
#
styles/prosilver/template/overall_header_body.html
#
#-----[ FIND ]------------------------------------------
#

Somewhere in the header that you think would suit

#
#-----[ AFTER ADD ]------------------------------------------
#

     <span class="tweet-link"><a href="http://twitter.com/home?status={TWEET_PAGE}" class="tweet-link" title="{L_TWEET_PAGE}"></a></span>

If you have already installed "Tweet this topic/post", then you can skip the next 2 steps and go straight to purging your cache

#-----[ OPEN ]------------------------------------------
#
styles/prosilver/theme/colours.css
#
#-----[ FIND ]------------------------------------------
#

    a.right:hover {
       color: #5E7BAA;
    }

#
#-----[ AFTER ADD ]------------------------------------------
#

    .tweet-link a {
       float: left;
       background-image: url("{T_THEME_PATH}/images/twitter-logo.png");
       padding-left:18px;
       height: 18px;
       background-repeat: no-repeat;
       position: absolute;
    }

Place this image in your ./styles/STYLE_NAME/theme/images/ folder