Today my colleague and I ran across two vendor supplied machines running IE 6.0 (we're not supposed to update them) that we needed to get connected to the Internet for the vendor's support. Our proxy server, Ironport WSA, has an issue when used transparently with IE 6.0 that requires you to explicitly configure it as the proxy server. Unfortunately the vendor had disabled access to the LAN Settings even to the Administrator login.
Thankfully, you can't disable the registry. There are two ways for these settings to be disabled. The first is as an all users setting and the other is per user.
To enable the settings if done for all users open regedit and go to:
HKLM\Software\Policies\Microsoft\Internet Explorer\Control Panel
In that key will be two values, Proxy and Connection Settings. Set both to 0 to enable the settings.
The per user setting is in a similar path in the user hive.
Likewise the keys need changed to 0.