Installing Device Driver software silently can present additional challenges compared to a standard application.
When you install the drivers manually, do you get a message saying that the drivers are unsigned and have to OK the install in order to proceed?
Current windows operating systems eg XP to Windows 7, are increasingly resistant to allowing installs of any content that could compromise security, and therefore having drivers that are code signed is really important if you plan to undertake silent installs. If the drivers are not code signed, contact the suppliers and explain your requirement for silent installation and see what they have to offer.
If you need further advice, please give us more details of the drivers and if they are downloadable, include the URL.