https://www-secure.symantec.com/connect/articles/do-i-have-correct-driver-winpe
http://www.symantec.com/business/support/index?page=content&id=TECH110134
http://www.symantec.com/business/support/index?page=content&id=TECH122799
The above articles cover the process of validating and adding drivers to WinPE V2. However, newer hardware is not offering Vista drivers, so unless you are able to source these drivers from the chip manufacturer's website, you may wish to follow the process in the following article:
https://www-secure.symantec.com/connect/articles/creating-and-using-winpe31-image-gss-251
Check what NIC chipset your Lenovo machine uses - often it will be something like the Intel 82579. Searching this forum on 82579 will yield links to proven working drivers, as will searching on some other common chipset numbers.