Use a live distro to backup the stuff to an external disk, then boot off the windows install disk and run diskpart/clean from a command prompt, then proceed to install.
Download clonezilla or aomei backupper or whatever freeware tool you prefer, even the freeware version Acronis provided by WD should work, but remember to clone using the bootable rescue disk never clone from within Windows or you'll end with a drive letter mess...
You can use ABR (Activation Backup and Restore) to manually backup royal key and manufacturer certificate, that way you can clean install windows 7 and restore the key/cert any time you want, just install windows and skip entering a serial number.
May i suggest this awesome tool: Advanced Tokens Manager to backup your activation files, if you ever need to reinstall, do it offline and restore the files and windows is activated in no time.
This way works like a charm, tested with a promotional $14.99 upgrade key on a clean install with a new computer, no need to re-enter key after the rearm, on reboot it was already activated.
Exactly my feelings last week when I installed my mom's new HP ENVY, at first i was like WTF?? Then I was like MEH!! Not as fast as everyone says, only the boot process was shaved a few seconds.
Actually to wipe the first sectors of the disk just run the "clean" command alone, if you do a "clean all" it will zero the full disk and will take a while.