Use the free GParted Bootable CD
which you can make from the downloadable ISO file from here: http://gparted.sourceforge.net/
To make the bootable CD from the small ISO file, you can use IMGBurn:http://www.filehippo.com/download_imgburn/
With GParted, basically all you need to do is delete the existing partition. No need to create a new partition at this point since your Windows installation DVD can do that.