勉强能用吧

topic_search.js

// ==UserScript==
// @name       douban topic search
// @namespace  http://www.douban.com/update/
// @version    0.1
// @description  provide a topic search entry
// @match      http://www.douban.com/update/*
// @match      http://www.douban.com/*
// @match      http://www.douban.com/*/*/statuses
// @copyright  holys
// ==/UserScript==

var searchForm = '<input type="text" name="q" id="inp-topic" class="j a_search_text search-query"  style="width:242px;font-size:14px;" \
   maxlength="36" value="" title="话题">\
  <input type="hidden" name="cat" value="1005">\
  <input type="submit" class="btn butt topic-btn" value="搜索话题">';


$(document).ready(function(){
  if (document.URL.indexOf('statuses') != -1){
      $('.aside').after(searchForm);
  }
  else {
      $('.extra').before(searchForm);
  }
});


$(".topic-btn").unbind('click').click(function(){

  //window.open("http://www.douban.com/update/topic/"+ document.getElementById('inp-topic').value);
  window.location.href = "http://www.douban.com/update/topic/"+ document.getElementById('inp-topic').value;
});