1.) Go back into Disk Management, select the unallocated space, right-click it, and choose to create a simple volume of it. The wizard will guide you through the process of re-creating the D: drive, this time letting you use it for additional storage, of music files for instance.

2.) Use partitioning software such as Partition Magic to recreate a partition of the unpartitioned space and then merge the two partitions. This entails some risk of data loss/corruption and can be costly.

3.) Use the recovery disks to reformat the entire hard drive and reinstall the OS. It's free and accomplishes exactly what you want, but it's time consuming and forces you to start from scratch again, losing all files and installed programs.

The choice is yours, which ever you think is the most viable.

John