Are you trying to move applications or data (video, audio etc.) files?
If you're just trying to move data files then just CUT and PASTE the files using Windows Explorer. If you want to move actual applications (ie. programs like Nero, WinAmp, MS Word etc.) then you will need to go into the Control Panel (Start ---> Control Panel) and then click on the "Add/Remove Programs" and uninstall each program one by one. Make sure you have the original installers or origianal CDs available. Once you've uninstalled your applications you can reinstall them again, except this time install them on your D: