My C: drive is nearly full and my D: drive has little on it.  How can
I move Picasa and my saved photos from C: to D:?

Try installing Picasa on your D: drive.   I installed Picasa on my
Maxtor drive and all is well.

I would also suggest to open Picassa, go to the tools menu, choose
options and on the General tab, change the destination for "Save
Imported Pictures In".  You can use Windows explorer to cut and paste
your picture files from your C: drive to your D: drive.  You can
determine where each folder is located by using Picassa...simply right
click on the folder and choose "Locate on Disk".