It is possible that windows 8 will not allow you to install Ubuntu by LiveCD/USB or Wubi. This is because Windows 8 introduced several new features, of which 2 are:
UEFI which substitutes what we have known as the BIOS (Is an alternative to)
Secure Boot which prevents anything but the installed operating system, in this case Windows 8 from booting.
See this article for installing Ubuntu on Windows 8.
Generally Speaking, there are two major ways of installing Ubuntu, without a CD.
You can create an ubuntu liveusb and install ubuntu on a dedicated partition (or inside a windows partition, this works as well). If you want to do this, see this article on how to create an Ubuntu live usb.
You can install Ubuntu via Wubi. Wubi is an windows installer for Ubuntu. Wubi creates a big file, let's say on your Windows where it install Ubuntu. The downside of using Wubi is that you cannot recreate a dedicated Ubuntu partition by using the wubi method.