For users who want to manage their partitions under Windows Vista or Seven, without downloading any additional software, the follow the below procedure:

The procedure is the same for the Windows XP/Vista and 7:

Click on Start > Right click on Computer (My Computer) > Manage.

In the Computer Management section, go to Storage > Disk Management.

Note that: this option is not available under Windows XP.

Right-click the partition to divide > "Shrink Volume ..."

A window appears asking you how much space you want to use for the new partition.

Click on Shrink

You now have an unallocated space.

To use this space, you will now need create a new partition or expand an old one.

Right-click on the "unallocated" disk space

Select "New Simple Volume".

A wizard window will open.

Follow the on-screen instructions.

Assign a drive letter to your newly created partition

Note that: this option is not available under Windows XP.

A wizard window will open.

Follow the on-screen instructions.

Deleting a partition will erase all data on this partition!

To delete a partition:

Right-click on the partition and select Delete Volume ...

Click on Yes to confirm.