As Dan already wrote, server 2008 R2 does not have native NIC teaming. You can team NICs only if the vendors driver supports this. Some do, some do not.
As for your specific NICs. Just stating that it is a Broadcom is a bit to generic. Much akin to "I need to repair my cars battery. It is a Volvo", without specifying a specific model.
Searching for Dell R320 NIC makes me suspect that you are using the Broadcom NetXtreme. According to this FAQ on the Broadcom website you can team those as follows:
In the Control Panel, click Broadcom Advanced Control Suite.
Select Teams from the menu, and select "Go to Team View".
To create a new team, select Create Team from the Team menu
or right-click one of the devices in the "Unassigned Adapters" section
and select Create Team.
A teaming wizard will display. Follow the instructions in the wizard and
and then click Finish to create the desired teaming configuration.
If you did not yet install the Broadcom drivers, do so now (sometime windows will find and use its own drivers, and then functionality will differ).