With Windows Vista, Microsoft dropped support for the AMD PCNet card that legacy versions of used to provide as the default virtual network card. For Windows Vista guests, now uses an Intel E1000 card by default.

If, for some reason, you still want to use the AMD card, you need to download the PCNet driver from the AMD website. This driver is available for 32-bit Windows only. You can transfer it into the virtual machine using a shared folder. See Shared Folders.