In windows explorer switch view to show hidden and system files. Look in the Windows folder and there will be a lot of files starting $ntwindows...etc - in blue text, not the usual black. All these can safely be deleted. They are leftovers from updates.
Also on C drive look for any folders that are long strings of numbers - again these can be deleted as they are leftovers from updates.
Just checked my W7 home premium installation 27GBon a 60GB partition. I use this as a media centre so have dual tuners installed and MS office. All data and recorded tv is on separate partitions. So not sure what is filling your hard drive.