I see my mate theog has a good idea, but first I would wipe secure erase
just the Linux partition using the free bootable Partition Wizard CD to see if that will do the job, it may be a lot better than simply deleting the partition in Windows 7 disk management.
Have a look at Option Three of this tutorial at the link below ... Partition Wizard : Use the Bootable CD
Then be sure to get the PWBD and not the installed version; scroll down to see the download link for the bootable CD ISO file at this link below. Partition Wizard Free Bootable CD
Then use ImgBurn to burn the ISO to a CD, at no greater than 4x speed with a verify; it was designed for use and works best from a CD rather that a DVD then boot
the created CD to run the wipe. ImgBurn Free ISO Burning Software