I have just copied my Ubuntu 64bit ISO into my USB Flash Drive and booted from there. It's my first time using a Linux distro, right now I'm using Windows 8 and writing this from the Try Ubuntu option. I'm just trying to install Ubuntu along with Windows 8, to keep both and select which one I want to start when I turn on my machine. I know there are similar questions, but no one helped me.

I execute the GParted program to make a partition of the hard disk. This is what I have.

Can you see the red icon at the /dev/sda2 partition? That's the Windows 8 system, and the sda1 is the Windows 8 booter (as far as I know). I do right-click on the sda2 partition and try to reduce the size to something like 700mb to let 300mb to my new Ubuntu system. But it's locked. It doesn't let me to resize or touch anything. It let me when resizing the sda1 partition but not the one with the red icon.

This is what I'm getting while doing Right-click > Information on /dev/sda2.

I'm very very new in this Linux-based world, so, how can I make a new partition to install this beautiful operating system?

Thanks a lot.