我看了一下代码,那个config.php是根据你填的内容写的啊
你确定你的内容都对?
<?
      include"lib.php";
      head();
      if(file_exists("config.php")) error("config.php文件已经存在.<br><br>若要重新安装,安装前请删除config.php文件!");
?>
<script>
 function check_submit()
 {
 if(!write.hostname.value)
 {
   alert("请输入主机名");
   write.hostname.focus();
   return false;
 }
 if(!write.user_id.value)
 {
   alert("请输入MySQL用户名");
   write.user_id.focus();
   return false;
 }
 if(!write.dbname.value)
 {
   alert("请输入MySQL数据库名");
   write.dbname.focus();
   return false;
 }
 return true;
 }
</script>
<body bgcolor=#000000 text=#ffffff>
<br><br><br>
<div align=center>
<table cellpadding=0 cellspacing=0 width=600 border=0>
<tr>
 <td height=30 colspan=3><img src=images/inst_top.gif></td>
</tr>
<tr>
 <td>
   <br>
   <img src=images/inst_step2.gif>
 </td>
</tr>
<tr>
 <td>
 <br>
<form name=write method=post action=install_ok.php onsubmit="return check_submit();">
<table border=0 cellpadding=2 cellspacing=0>
<tr>
 <td width=90 align=right style=font-family:Tahoma;font-size:8pt;>主机名</td>
 <td width=90><input type=text name=hostname value='localhost' style=font-family:Tahoma;font-size:8pt;></td>
 <td width=300>请输入数据库的主机名.</font></td>
</tr>
<tr>
 <td align=right style=font-family:Tahoma;font-size:8pt;>MySQL用户名</td>
 <td><input type=text name=user_id style=font-family:Tahoma;font-size:8pt;></td>
 <td>请输入MySQL的ID</font></td>
</tr>
<tr>
 <td align=right style=font-family:Tahoma;font-size:8pt;>MySQL密码</td>
 <td><input type=password name=password style=font-family:Tahoma;font-size:8pt;></td>
 <td>请输入MySQL数据库的密码</font></td>
</tr>
<tr>
 <td align=right style=font-family:Tahoma;font-size:8pt;>MySQL数据库名</td>
 <td><input type=text name=dbname style=font-family:Tahoma;font-size:8pt;></td>
 <td>请输入MySQL数据库名</font></td>
</tr
><tr>
 <td colspan=3 align=center><br><br><input type=image src=images/inst_b_2.gif border=0 align=absmiddle></td>
</tr>
</form>
</table>
<br>
</td>
</tr>
</table>
<?
      foot();
?>