First of all, the only difference between Ubuntu and Kubuntu is that Ubuntu comes with the Gnome desktop and Kubuntu comes with KDE. Both desktops can be installed on either OS - or really any other version of Linux. So you don't really need both installs on the same machine.
You don't install on "root". Root is simply a mount point for that installation. Root has to reside on a partition somewhere separate from the other installs. When you install, the boot loader goes on the MBR and is handled through /boot. So save partition space, Linux installs can share partitions such as /swap.
If you perform the installation correctly, you should be able to see all four OS's at the boot loader menu. Windows is usually listed as "Other",which can be renamed later. Any Windows OS's should be installed BEFORE any Linux installs.
I'm not aware of any how-to's off-hand, but you should be able to Google "linux dual boot" and "linux grub" to find out how that all works.