I would like a Python operating system to replace Windows--that I can tweak or add to. I am so sick of Windows. Why isn't there something?

Have you tried linux or freebsd?

The One Laptop Per Child (OLPC) project wrote Sugar to run on its laptops. Sugar is an Operating System written in Python. Sugar is a quite different to other Operating Environments. http://wiki.laptop.org/go/Sugar

Actually, Sugar is a User interface (UI) that lives on top of linux. Python is a scripting language, and by definition cannot be used to create an operating system because it requires an operating system underneath it.

I think what you might actually want is a replacement for Windows, that includes Python as a scripting language, and the answer to that is Ubuntu, Fedora, or almost any other current version of linux. Just download the USB image or install iso and burn the disk, then load it onto your PC. Then use the App Installer to generate the overall environment you are looking to create. This could include Python, Perl, various UI's or desktops, various shell environments (bash, ksh....)