If you have an 11G or newer Dell Server (for example R61x, R71x, R81x) then you should use the Dell LifeCycle Controller:
Step 1) Update the LifeCycle controller OS drivers pack:
The Dell LifeCycle controller keeps a set of up to date drivers that will be used by the operating system during install.
Step 2) Install the OS:
launch the Dell LifeCycle Controller, select the OS you wish to install and follow the onscreen instructions. The LifeCycle controller will slipstream Dell drivers into the OS installation (it’s a good thing you updated those in step 1).
Note: the Dell LifeCycle controller OS driver pack will copy drivers from it’s internal repository to a temporary folder that is used by the OS installation. This temp folder is deleted/removed after 18 hours or upon power cycle of the system.
If you have an PowerEdge Server 10G or older (for example a PowerEdge 2950), you should use the Dell System Build and Update Utility (SBUU):
Step 1) http://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=YH0GX