There are many softwares to Re-partition the hard disk for windows operating system. But for windows vista you do not require partition software because windows vista comes with Disk Management software.

Steps to Re-Partition

1. Login as administrator.

2. Navigate to Start -> right click My computer -> Manage

3. Computer management will be opened

4. Select “Disk Management” under “storage”

5. Right-click the volume you want to shrink, and then click Shrink Volume.

YouTube Tutor Video which explains how to re-partition hard disk in Windows vista.