The way to identify the right driver is fairly simple.
1. First Identify the right PNP_ID (DEV_ID) of the device.
If you are already inside Windows, then go to device manager-->properties--> Details -->Under Property select "Hardware Ids" and Make a note of VEN_XXXX and DEV_XXXX
2. With the identified VEN and DEV ID's locate the right chipset ( I normally prefer http://catalog.update.microsoft.com or www.pcidatabase.com to look up for the right chipset and driver)
3. Once the chipset is identified using VEN and the DEV ID's . You can visit the vendor site and download the driver for that chipset and also, you can open the driver inf file and search for the same DEV_XX which you grabbed to make sure it has the ID matching. Also, you can verify the driver has the right architecture by looking at the [Manufacturer] section from the driver inf file.
4. Import the driver to MDT and rebuild the WIM.
5. If you say, the machine has nothing installed and you need to identify what it has, then booted using MDT 3.0 PE. VEN_ and DEV ID's info are available from registry
The above process may sound really complex, but it actually take less than a minute identify the unknown device once you try it.