I have 2 drives C:\

Question

I have 2 drives C:\ and D:\Im trying to reinstall my windows but my c drive would not allow me to do so. Instead I could only do so on D:\Now I have three options during bootup: c:\Windows, D:\Windows and Set up Windows XpNow, I have installed windows on my D:\ drive, I would wish to format my C:\ However I am unable to do so because the system says there are setup files on C:\ so Its not possible.Please help. I want to reformat my C:\