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.