Having a Windows CD would definitely be a good thing. However, here's a suggestion for moving your OS to the larger drive without having a Windows CD. Can you backup the pictures on the larger drive to a CD or other external media so that you can format, i.e. erase, drive D? Hard drive makers have software tools to copy the full contents of one drive to another; such software is often put on CD and packaged with new hard drives. For example, Western Digital's Data Lifeguard Tools can do this, at least for Western Digital drives.
If you can use such software from one of the hard drive makers, you could copy your OS to your larger drive. Then, make it master, or C, and the smaller drive could then be used as a slave drive, i.e. D.