just em, there is an igb driver (this follows behavior with our Linux drivers).
All adapters up to the 82575 are supported in em, and new client/desktop support
will continue to be in that adapter.
The igb driver is for new server NICs like the 82575 and its followons.
Advanced features for virtualization and performance will be in this driver.
Also, both drivers now have shared code that is up to the latest we have
released. Some stylistic changes as well.
Enjoy :)