求助:怎么让这个搜索框的文字垂直居中。

<script>
function search4()
{if(form1.nsns[0].checked)
window.open("http://www.baidu.com/baidu?tn=site37021&wd="+form1.key.value,"mspg0");
if(form1.nsns[1].checked)
window.open("http://www.google.com/search?hl=zh-CN&inlang=zh-CN&ie=GB2312&oe=GB2312&q="+form1.key.value,"mspg4");
if(form1.nsns[2].checked)
window.open("http://www.sogou.com/web?query="+form1.key.value,"mspg1");
if(form1.nsns[3].checked)
window.open("http://www.soso.com/q?w="+form1.key.value,"mspg10");
return false;}
</script>
<div id="search">
<form name="form1" id="form1">请输入关键字：
<input class="kw"  size="15" name="key" />
<input class="llb" type="submit" value="搜索" name="B2" />
<input type="radio" checked="checked" value="0" name="nsns" />百度
<input type="radio" value="google" name="nsns" />谷歌
<input type="radio" value="2" name="nsns" />搜狗
<input type="radio" value="soso" name="nsns" />soso
</form>
</div>  
这个搜索框在IE6、搜狗浏览器下，输入的关键词垂直方向不居中，请问怎么修改？