While you need to wipe the entire drive with a program like DBAN or something that writes over every bit, it is simple to wipe the restore points.
Just open the system control panel, click on system protection, select the system protection tab, then select the drive and turn off the restore points using the configure button and click OK or save all the way out.
Unfortunately, Microsoft took down the downloadable ISO images of Windows 7 some time ago, so if you don't have one you cannot do a clean installation. The product key is no problem, if it is not printed on the label on your machine you can easily recover it using a free tool like Belarc Advisor, but you would still need an installer disk. If the data is not sensitive, it...