终于写出个有用的东西了！
能够检测大部分通过代理服务器访问的ip.
<?php  
//beiji.com   2000.6.17  
$ip = getenv("REMOTE_ADDR");  
$v = getenv("HTTP_VIA");  
$f = getenv("HTTP_X_FORWARDED_FOR");  
$c = getenv("HTTP_XROXY_CONNECTION");  
$o = getenv("HTTP_PRAGMA");  

print '<br>REMOTE_ADDR';  
print $ip;  

if (($v=="")&&($f=="")&&($c=="")&&($o=="")){  
print "<br>not through proxy";  
}  
else {  
print "<br>through proxy";  
print '<br>http_via: ';print $v;  
print '<br>http_x_forwarded_for: ';print $f;  
print '<br>http_xroxy_connection: ';print $c;  
print '<br>http_pragma: ';print $o;  
}  
?>