VMware released a driver for ESX4 that supports the Quad NIC:
http://www.vmware.com/support/vsphere4/doc/drivercd/esx40-net-igb_400.1.3.19.12-1.0.4.html
Regards,
Tom
Drivers are obtained in two ways. InBox support, where VMware takes the Intel driver, customizes it for the VMware environment and puts it on the DVD.
The second way is through the I/O Partner Program. Using this mechanism Intel takes the standard driver for a product, modifies it for VMware environment, validates it and then provides it to VMware, who in turn validates it again and then publishes it on their support pages.
Hope this helps clear up how things are done.
