Format c: and Fdisk won't erase your HD.
Both can be EASILY recovered.
I have been up North visiting family this week and actually watched the 2 MIT guys on Tech TV.
They explained easy ways to recover data off either method. Even writing over data leaves trace amounts that could be recovered.
Tech TV online article
Ultimate Data Destruction article
The program they recommended on the air is called Autoclave.
Autoclave
It makes a boot disk, you boot with it then it completely wipes and cleans your HD.
Probably also fun to take over to your friend's house.
