cffraser,
The below link shows how to locate drivers for Winpe, at the bottom of this kb there are links to manufacturer driver packs that you can download.
Locating the correct network drivers for your client PC on Ghost Solution Suite
https://support.symantec.com/en_US/article.HOWTO124400.html
How To Add Drivers To Ghost Solution Suite
https://support.symantec.com/en_US/article.HOWTO124704.html