The USB 3 docks use DisplayLink's Ethernet, and PE suport is covered in the corporate install guide:
http://www.displaylink.com/corporate...UsersGuide.pdf
The USB 2.0 docks from Lenovo used the ASIX Ethernet (I think). The ASIX Ethernet drivers should be separately available from the ASIX website:
http://www.asix.com.tw/
Although at the time of posting their website appears to be down.
Wim