<?php

function search_rank($keyword, $target, $max_request = 1) {
    $dom = new DOMDocument;
    $url = 'http://search.yahoo.co.jp/search?n=100&p=' . urlencode($keyword);
    for ($i = 0; $i < $max_request; ++$i) {
        @$dom->loadHTMLFile($url);
        $xpath = new DOMXPath($dom);
        foreach ($xpath->query('//*[@id="web"]/ol/li/a/@href') as $j => $node) {
            $value = preg_replace('@^https?+://@', '', $node->nodeValue, 1);
            if (strpos($value, $target) === 0) {
                return $i * 100 + $j;
            }
        }
        if ('' === $url = $xpath->evaluate('string(//*[@id="pg"]/a[string()="次へ »"]/@href)')) {
            break;
        }
    }
    return false;
}

$keyword = 'mpyw';
$target  = 'twitter.com/mpyw';
var_dump(search_rank($keyword, $target, 2));