As noted on http://knockoutjs.com/documentation/observables.html, optionally you can pass a second parameter to ko.applyBindings to define which part of the document you want to search for data-bind attributes. For example, ko.applyBindings(myViewModel, document.getElementById('someElementId')). This restricts the activation to the element with ID someElementId and its descendants, which is useful if you want to have multiple view models and associate each with a different region of the page.
Another option would be to use the with: binding introduced on ko 1.3+, which renders the DOM based on a specific viewModel property. This is nice because if the property is null, nothing is rendered at all. Steve shared a live example about this feature on http://jsfiddle.net/StevenSanderson/f5w6u/3/light/