>But, the only problem with that is the following. This is why I avoided to use it. I wanted to restrain the resizing under 1256 pixels, assuming the body.client area was that size. But, if the window would have been smaller at first, this would restrain the user, or lock the environment at 1000 pixels for example, blocking the user from the possibility to resize back to a higher width.

Did you consider CSS properties min|max-width?
http://www.w3.org/TR/CSS21/visudet.html#propdef-min-width

Major browsers should support it
http://www.webdevout.net/browser-support-css

You can change it by JavaScript, e.g. document.body.style.minWidth