Some of the things you mentioned I would not know how to do. I guess I can't simply save the partition to a data disk, and then boot from it and load the OS/settings onto the PC after a dban wipe, can I?
Practical answer: First, boot the machine to the recovery console that uses the manufacturer's hidden partition to restore the OS to its initial state. "In theory," this will erase all of your private data, since it resets the system to the condition in which it was shipped to you.
Second, install and run any freeware tool to "wipe" freespace by overwriting it several times with a succession of patterns. This will wipe out any data was stored in parts of the disk that are now marked as being unused but may still have your credit card number and love letters in them. Try this tool: http://www.fileshredder.org/
Commentary:
The idea is that every sector that is used will have been written by the recovery process, and every sector that is not used will be overwritten with garbage. This guarantees that
all of the old data is destroyed.
Other members: Will the re-install be enough to wipe out the contents of the pagefile, which may contain just about anything? I think that it will, but please help inhalexhale_1 out here if I am giving bad advice.
Technical answer: The way a PC boots up typically involves three steps. The BIOS, which lives on your motherboard, initializes this-and-that and looks for the first disk that is tagged as bootable (by having an "active partition"). The BIOS then runs the small program that it finds in the disk's Master Boot Record (MBR), which was created when the original OS was installed. This MBR is not associated with any partition. The program from the MBR, which is not necessarily specific to any operating system, chooses a partition (it may offer you choices) and then loads the Partition Boot Record (others: is that the correct term?) which is specific to the OS and actually loads the OS.
So if you save the partition and wipe the disk, then restore the partition, you will have no MBR for the BIOS to hand off to, and the PBR will never get loaded. Moderately advanced skills, and lots of practice, may be needed to create a new MBR and have it hand off to the restored PBR.