Issue:

My current ESXi 5 rig is based on an Intel DH67BL Motherboard, which makes use of an Intel 82579V Gigabit Ethernet Controller. This unfortunetly (at time of writing) does not appear when installing ESXi 5.

Rather than having to purchase another NIC, the onboard Ethernet can be enabled by installing the needed drivers to the standard ESXi installer. Follow instructions here: http://www.ivobeerens.nl/2011/12/13/vmware-esxi-5-whitebox-nic-support/