My issues are resolved! 
I just opened two windows, one with the D:\ files and one with the C:\ files. Then
carefully used
drag-n-drop to move the D: files to their proper locations in the C: files. I tested each program, as I went, making sure I didn't screw up anything... like dropping it in the wrong location. Each one worked the way it used to.
Just found this post from IainB.
Maybe this download includes a solution to my issue? 
-crabby3
I tried this first but... it didn't help or change anything that I could find.

Crabby, if you're not sure what you're doing, and you'd like to revert to how things were, you could consider using System Restore.-tomos
I tried this second... unfortunately this didn't help either... but I was able to learn what to expect from Vista's System Restore.

The only noticable change was... the DATA (D:) file name, on the Start Menu's right pane, reverted back to Documents... but all the files (that I had moved) were still in D:\
I still have the
original issue though...

...running out of disk space on C: ... but I think I'm through with moving stuff around to get it.