Since the dawn of time, Windows PE (WinPE) has not had any support for the 802.1x authentication protocol. This meant that any network deployment of Windows via a network secured with 802.1x was a non-starter, causing headaches for a few on my customers; I actually had one customer that ran new network cables to a majority of the desks in order to be able to deploy Windows XP over the network.
The Deployment Guys : Added support for 802.1x in Windows PE