I am trying to move from VMware Fusion to VirtualBox since Fusion 3.0 is not working since I upgraded to Mountain Lion. VirtualBox is working but I cannot connect to the Internet on my guest OS (Windows XP). I am new to VirtualBox, so any help will be appreciated.
Be sure that you have installed the latest version of Guest Additions to the VM
Turn off the VM
Under the network adapter configuration choose bridged mode
Then click in advanced and change the adapter type to Intel PRO/1000 MT Server (82545EM). -Be sure to enable the checkbox "Cable Connected"
Worked for me, hope it helps