@THXTEX: if your drivers come with a .CAT file they should be WHQL. check setupapi.log in your WINDOWS folder see if you can find the device or the .INF you are trying to install.
@Mengha: it doesn't really matter what folder you put the drivers in. organize it as you see fit. just make sure the OemPnPDriversPath in your WINNT.SIF matches where you put the drivers.
@THXTEX: try removing %SYSTEMDRIVE% from the OemPnPDriversPath entry. i believe it should look as follows: [Unattended] OemPnPDriversPath="Drivers\Chipset;Drivers\Lan" are those drivers WHQL certified?
i tried appending the OemDriverPathName entry with no success. the following two formats failed: OemPnPDriversPath="PATH1","PATH2" OemPnPDriversPath="PATH1;PATH2" it seems this method is limited to a single source path.