I'd strongly disagree with that suggestion. The reasons that people need Windows (for example playing games) tend to place greater demands on the hardware than Linux. If you have to run one OS natively and the other emulated then it is alomost always the better choice to emulate the Linux session. The better solution, of course, is to dual-boot.
OP. Presumably you have configured a network adapter in the VirtualBox configuration (I find it best to set the type of the adapter to "bridged"); this should appear as a network adapter in your Ubuntu setup and you just configure networking as you would on a physical machine. Are you having problems with this?