Create a volume set

Ok, here's the situation. I'm running WinNT Server 4.0. I have two physical hard drives. They used to be mirrored, but now I need more space so I broke the mirror and wanted to create a volume set. The first disk is partitioned into two drives (c and d). I created a volume set for the d drive with no problem using Disk Administrator. But when I went to create a volume set for the c drive I had a problem. It said "Disk Administrator can not extend the partition containin Win NT system files." SoI wanted to use Partition magic on the drive, but you can't use Partition Magic on a WinNT server machine. All I want to dois to create a volume set for the c drive. Any help would be greatly appreciated.