I got pissed off when I saw that my GIMP was separate, the tools where a window and there was no window controller.
It was just scattered all over the place.
I found this and I think it will help a lot of people operate GIMP with peace.

Open Terminal :

Type this in or copy it and paste it :

sudo apt-get install xnest metacity gimp

And now to test it, type this in :

Xnest :1 -ac -name GIMP -geometry 1024x690 & metacity --display :1 & gimp --display :1

Now it should run in a whole window, you don't need to use that code to run gimp every time, that's it, just run gimp normally and it will be in one window.