If installation fails them something is definitely wrong with driver signing. We have customers who initially have signed drivers following Microsoft guide, but something was missed and installation failed.So far each such case was successfully resolved. Try to install signed drivers manually (through the Local Area Connection properties) to see if system complains on signing.
Note, that for the NDIS IM drivers you have to sign both CAT file and driver binary (embedded signature). May be this the case.
Creating an absolutely silent installation is possible, but prior to installing driver you have to install your certificate as trusted one. In this case system won’t ask user if he trusts the particular vendor during driver install process. This is not recommended by Microsoft. though.