Need to free up D drive...please help?

About a month ago my PC crashed and using a windows xp cd that i got from an old case of cd's i installed windows again...doing so on my d drive by accident as i hurriedly needed to retrieve important files....upon opening up windows newly installed, none of my programs were installed however my files were there....A month on and my d drive (21.05 GB) is completely full, not even allowing me to run disk cleanups and download security updates for norton internet security 2010....i also get frequent "low disk space" notifications for my d drive which is now home to "doents and setttings", "program files" and "WINDOWS"... my C space meanwhile has 69% of its space free (89.2 GB)..... is there any way to move data from my d drive to my predominantly vacant C drive.....ive tried this in safe mode but i am not allowed to do this......can anyone offer any solutions??