More on moving data to Alternate Libraries on Drive D:
By default, any dragging and dropping, when crossing a drive letter boundary is a COPY. This makes sense because the most common uses of extra drives is for making a back-up or for putting a file on a flash drive and in these cases you generally don't want to delete it from your C: drive.
Now before I offer the solution of how to move I would add this caveat, unless you are a rather experienced user, it would probably be safest if all you move is some of your data (documents, music, videos, and pictures), not windows files, because you could really mess things up.
Anyway, when you drag your data files over to the D drive, hold down the SHIFT key. You should see the text in the popup window change from COPY file to MOVE file. Of course, for files you already COPIED, you can simply delete the original that is still on the C: drive (as I said, just don't delete W7 system files and folders).
A couple more tips:
1)if you do start storing data on the D: drive I recommend you create a Folder on D: with your Userid and then folders under that for Documents, Music, Pictures, and Videos and then move your files under these folders, that way you maintain the data structures W7 uses. (If you ever get a network and have to share/lock folders etc this can make things easier and even if you don't it can help with my next tip)
2)if you decide to have some data on C: and some on D: then, if you use libraries, you will probably want to add your D: drive data folders to your libraries.
Best way to explain what I mean is with a picture of mine ...
As you can see I have My Videos (which is the default folder on the C: drive) but I have also added several folders on my D: drive.
To do that you simply
right-click on the library type (Documents, Music, Pictures, or Videos) and choose properties and there you add additional folder(s).