I`m not quiet sure what you mean.
First of all is the Ethernet adapter your talking about on the motherboard.
Or is it a Pci type fitted to a slot in the server tower.
If it`s a case of the Ethernet on the motherboard. Just look up the mobo name and model number and Google it for the drivers.
If the Ethernet card is of a Pci type you can find out the brand of chip set used and the revision, google the both.
You also need to check what version windows server 2008 is. 32 bit or 64 bit.
If you try to install a 32 bit it will refuse saying it is wrong.
And vice versa.
Windows Server 2008 Device Manager
May be your best option if the driver you have is not a .exe or auto install.
But extracts to a folder inside the folder should be a .inf file.
Use device manager if the case, and where it says unknown devices, or if one listed in the section it is most likely the Lan adapter.
Or if it lists it as an Ethernet adapter but has a yellow exclamation mark next to it.
Right click on either. And select update driver, select browse for driver.
Click inside the folder, if the .inf file displays click on it and select ok.