Getting back to the original point of this thread...
Thank you for your replies, but installing even the full install of DirectX and not the web download version gives the same message about files being in use. I can't get around this problem, no matter what I try. A reinstall of Windows Vista is not an option, unfortunately.
Any further suggestions?
EDIT: Oh, and I tried just copying the file, but it did nothing. Since that file was from an older update (that obviously never took) and not the November one, does the core .dll file not read it? Also, I tried booting from the Vista CD and running from command prompt, and it gave me an error also and said to look at the error .txt file, but none was created.