Pulls on flame proof suit...
Formatting should be a last resort. Installing a new copy of Windows will copy the existing Windows and Program files folders and install a brand spanking new version. The Microsoft migration tools for apps and settings work well and for other apps like Thunderbird, I always set these up to store data in My Documents somewhere rather than under Application Data.
I've done this many times since XP SP2 when it got really stable. I leave the old folders hanging around for a week or two until I know I've got everything then delete them.
With a little work, it's very easy to segment OS, applications and data just as well as using a separate partition.
I still reckon there's no value in partitioning for a single OS and in my experience, causes far more problems than it ever solves. I also reckon that the security angle is a red herring. Can't think of a single security advantage.
My advice would be to not partition but to spend 10 minutes thinking things through then using what is already there to segregate data.
Finally, Windows can do all of the partitioning for you. When you say you are running as admin, are you sure? Or did you just add your account to local admins? They are not the same thing! To partition as admin, type cmd in the search bar, then right click Command Prompt and click Run as Administrator. At the command prompt, run mmc. Add the Disk Management snap-in (File->Add/Remove snapin).
Regardless, good luck with the build.
Cheers
Simon