Restore partition on Dell 1520

That D partition brings you back to the original settings, you had, when you bought your computer. You can delete it, since the Discs that you received with your compueter have the same information, it was created by Dell.
If you already installed Win 7, there should already be a sep restore partition, now.

1. Just delet the partition. It will become free space. No need to keep it as a separate partition, unless you want to
2. In computer management
3. If you're prompted for an administrator password or confirmation, type the password or provide confirmation.In the left pane, under Storage, click Disk Management.
   Right-click the volume, such as a partition or logical drive, that you want to delete, and then click Delete Volume.
4. Click Yes to delete the volume.

If you delete a primary partition, the resulting empty space is called unallocated disk space . If you delete a logical drive within an extended partition, the resulting empty space is called free space. You can now use the empty space to create additional volumes. To learn how, see Create and format a hard disk partition.