Did you have both Norton and avast! installed in the same computer?
Or, otherwise, you use NAV in a CD to scan your system?

You can reinstall Windows in one partition and do not ‘touch’ the other, specially if you want to install in the C: partition. Your data will be safe and you will be able to recover it after the reinstall.

To install Windows in another partition than C:, you must check this at the early beginning of the installation if I’m not wrong.

Good luck.