You also need to uninstall the "Rapid Restore" utility in Windows. That software automatically hides any drive that is labeled "D", so the paritition will be hidden in Explorer even though you'll be able to see the it in Disk Management.
Of course, you could just change the drive letter on the partition, but that causes problems of it's own. If you add something like a USB Thumb Drive or CompactFlash card in the future, IT will get assigned as D and will ALSO be hidden until you change the drive letter. Learned that one from experience, what a pain!