I imagine there are several ways to accomplish this. You might also take a look at the MS dism utility (Deployment Image Servicing and Management). It's in the Windows 7 AIK, which is a free download from MS. Windows 7 drivers need to be loaded into a protected area called the driver store, which is easily accomplished by script using dism. In my environment, we call dism (from a network share) in a cmd file using a syntax like this:
<path to dism>\dism /Image:D /Add-Driver /recurse /Driver:<path to drivers>
We run dism after applying the image (wim), but before the first reboot. Since the image was applied it is a live file system and no longer an image, which leads me to believe that it should also work to use dism in a scripted install. In other words, use "/Image" in the above syntax to point to the drive letter of the drive on which you installed Windows.
Good Luck!