Avoid using automatic-anything on a computer that already has an OS installed on it.
What you should do, for example by using GParted from a Ubuntu Live CD, is to re-size one of your partitions (preferably your largest) so that you shrink it. It will then leave x amount of unallocated space, which you can select and then use to create a brand new partition where you will later install Ubuntu on.
Repeat the process, but this time, create yet another partition that is slightly larger than your RAM.
When installing Ubuntu put it on the large empty partition you created above, using a ext filesystem. You will want to mount it as "/". Mount the other smaller partition as "swap", and then start the install.
To answer your other question: Dual booting doesn't touch your partitions. To speak of dual booting is just to say that you have a computer with two OS:s on it, and that you, when you start it up, are allowed to choose which one you will boot up.