Do I need to create a partition when I install Ubuntu with the Windows Installer? The installation steps do not say anything about this.
Installing Ubuntu with Wubi, the Windows installer, does not involve creating any partitions or modifying your existing partition layout in any way. This is one of its advantages, though if you want to use Ubuntu a lot or as your primary system, you might consider doing a standard installation alongside your Windows system (which does require repartitioning, though the installer can do it automatically for you).
See the official Wubi installation instructions for more information about how Wubi works, how it gives you an Ubuntu installation without needing repartitioning, and how to install it.
Wubi is an alternative method of installation for new Linux users. The whole process of Wubi, from start to finish, does not involve any partitioning, At All. What it does is that it creates and installs Ubuntu files within the Windows partition and the NTFS File System used by windows. There is good and bad to this.
Provides easier installation of Ubuntu.
No Partitioning, saving some load, stress and life on your hard drive.
Easy Uninstallation via The Windows Control Panel under Add/Remove Programs.
Slight performance loss when compared to the partitioned Ubuntu.
No Hibernation support (I don't use it anyway).
Maximum of 32 GB in installation size.
If you like using Ubuntu, then you can install it the partitioned way.