XpressConnect can detect the IE setting for specifying a proxy configuration file.
Supported settings include:
Unchecked - Default. When unchecked, IE will not attempt to retrieve a proxy configuration file from the URL. If unchecked, the URL does not need to be specified.
Checked - When checked, IE will retrieve a proxy configuration file from the URL specified. If checked, the URL of the proxy configuration file must also be specified.
XpressConnect is able to auto remediate this setting. By default, Windows XP and Vista has this setting unchecked.