Some times (most times?) migrating from VMWare to VirtualBox can get quite complicated. Mounting a disk from one into the other nowadays usualy works but network stuff seems to break more often than not.
Here's a little tip for those times when you are trying to get the network for a VMW image working in VBox: try using the third network adapter, that seems to be the same PCI address VMWare uses (in my machine... results might vary).