If you want to do something other than delete everything on the drive and create a single partition you will need something more than the winnt.sif answer file. With an answer file you can either delete everything and create a single large partition and install, or it can be set to install to the first partition that does not already contain an installation of Windows. If you want to create additional partitions you either need to create them before the installation using Windows PE or DOS. Or have the installation stop at the disk partitioning screen and partition it manually, though it will only format the partition that you install Windows to.