This is my config file, im sure you can tweak it yourself.
You can set IE to look at this in group policy or by DHCP, i use group policy.
Code:
function FindProxyForURL(url, host)
{
//Declare proxy strings as variables
var schoolproxy = "PROXY 172.16.16.52:8080";
// IP not to use proxy
if (shExpMatch(url, "*172.*")) { return "DIRECT"; }
if (shExpMatch(url, "*10.*")) { return "DIRECT"; }
if (shExpMatch(url, "*192.*")) { return "DIRECT"; }
if (isPlainHostName(host)) { return "DIRECT"; }
// URLS not to use proxy server
if (shExpMatch(url, "*website.com*")) { return "DIRECT"; }
// Slect Proxy Server
if (isInNet(myIpAddress(), "172.16.16.0", "255.255.252.0")) { return schoolproxy; }
else
return "DIRECT";
}