When a drive is totally overwritten, it no longer has any partitions defined. You or he will need to run Fdisk from either a boot-floppy or a bootable CD. Fdisk will see the physical drive (not yet as C, and you will need to define at least one partition for it and then reboot, again to the boot floppy or CD. Then you can format the drive so that it can be used.
Alternatively, if you have a Windows install disk, it will recognize the physical drive and allow you to partition the drive and format it.
With both of these methods, if you have more than one physical drive, make sure you are choosing the correct drive.