<p>I'm sure you've all seen them.  Line of Business UIs that have logic such as: "When ComboA is selected, query for values based on that selection, and populate Textbox B", or "When ButtonC is pressed, disable Textboxes C and D", and on and on ... it gets particularly bad when you can have multiple permutations of the logic above.</p>

<p>If presented with the chance to redesign one of these lovely screens, how would you approach it?  would you put a wizard in front of the UI? would you keep the single screen paradigm but use some other pattern to make the logic of the UI state maintainable? what would be the process you use to determine how this would ideally be presented and implemented?</p>

<p>Not that I think this should matter for the responses, but I am currently presented with just this "opportunity", and it's an ASP.NET web page that uses javascript to respond to the user's choices, disable controls, and make ajax calls for additional data.</p>

Start with the KISS principle, and work from there. Don't over-engineer the solution, and try to think about the problem from the user's POV. Your first impression of what would make a good layout is probably close to what you should be building, as a good UI is intuitive.
That being said, single screen versus multiple screens, JavaScript or AJAX, it doesn't really matter. If it looks good, is easy to understand, and behind the scenes, is well commented and written with clear code, it works. It should be maintainable, so aim for modular code blocks with clear functionality.