You can have 4 primary partitions on your hard drive before you need to create logical partitions, which extends it out almost limitlessly to the extent of your hard drive's capability.
As for the question, any time you install any version of Windows, it will break Ubuntu's boot loader GRUB. You can install Windows 8 on a partition that has been resized through GParted (boot from Ubuntu live CD or live USB) but will then need to repair your GRUB.
This process can be a pain and requires some knowledge of Partition locations, Mount Points, and Terminal commands.
For your ease, I will include the command here to be entered into Terminal. Replace
XXX with the location of your partition. This can be found out from Gparted (typically /dev/sda1 or something along those lines).
sudo grub-install /dev/XXX
This will install GRUB from the standard repositories Ubuntu provides in their distribution. The command above will install GRUB to your partition and attach itself to the mount point for booting.
Keep in mind that doing this will bring you back to a GRUB boot loader. If you are trying to use another boot loader, be specific with the setup you are wanting to use in order of first to last OS (e.g. as a recommended setup: Windows 8/Windows 7/Ubuntu).