Yeah moving the files from the C drive helps a lot. All Mp3, AVi, JPG and other types of files can be safely moved to the D drive.
Always think that Windows runs from the C drive and other data stays on the D drive. That way you wont confuse things later. Also, programs dont need to be installed on the C drive to run, they can be run from the D drive in a Program files folder too. When you instal a program when it comes up saying target location i.e
C:\Program files\NortonInternetsecurity
Just change the C to a D and the instal will create the directory for you.