E7450 Windows 8.1 x64 SCCM - NIC driver

Windows 8.1 x64 standard OS install.wim doesn't seem to have the E7450 NIC driver built in.

I have downloaded the E7450 driver CAB from http://en.community.dell.com/techcenter/enterprise-client/w/wiki/7939.latitude-e74507450-windows-8-1-driver-pack  and created a new driver package for this, which I've added to the task sequence.

WinPE seems to be talking over the network happily, but when Windows 8.1 starts up it has no network showing, and I assume this is why it hasn't joined itself to AD or done any other part of the task sequence.

What is the correct way to resolve this, and how do I got about doing it? I am fairly new to SCCM so please give details of any steps necessarily. Thanks in advance!