>>3621393In PS, click and drag out a guide line to the 1000px mark. Make sure your rulers are turned on and set to pixels for this. Then repeat this for the other direction. Now you'll have a 1000x1000 pixel section marked off. You can then have Snap turned on with your square marquee tool and it will snap to the corners as you drag it out. Then just right click on the selection and use "Transform Selection" to move and change it as needed.
If you want something more automated, you can make this into an "Action". Turn on the Actions window (Window>Actions). Create a new "set" then in that a new "action." Name them what you want. Then click record and draw out a new 1000x1000 selection with the square marquee tool. Stop the recording. Now any time you want that perfect square you just click on that action and play it then move the selection around where you want it and crop as normal (Image>Crop).
>>3621396Shoo, fake ambush.