I just ran into a problem again trying to emulate windowxp images from microsoft.
Basically download the driver:
“NDIS5 Driver for Microsoft Windows Server 2003, Windows XP, Windows 2000, Windows ME and Windows 98” from amd.com website. Yes it will be there it is very hard to find but basically go to driver Catalysts then to drivers then network and refine your search until you get it. Then extract the file it is called V4.51.zip then:
The link is currently:
genisoimage -o driver2.iso V4.51/
And mount it as CD from your opened vbox running instance of windows xp. And install the pcnet drivers. That is it you now have network.
This guy helped me a bit here.