Can't Delete Volume

I wanted to reduce the size and the existing partition of my second hard drive in disk management and I succeeded in same which was notified by the file manager in the reports. But when I check the Vista Disk Management then it says that the partition was not reduced at all. Also Disk Management is notifying that I cant further reduce the drive? Above that when I go into disk managemtn, then the Delete Volume option is grayed out and is not available. So how do i delete this existing partition and reformat the drive, any suggestions?

You can use Diskpart that enables a superset of the actions that are supported by the Disk Management snap-in. The Disk Management snap-in prohibits you from inadvertently performing actions that may result in data loss. It is recommended that you use the Diskpart utility cautiously because Diskpart enables explicit control of partitions and volumes. More information can be found here - http://support.microsoft.com/kb/300415