If you are familiar with web programming today, Ajax isn't a tough technology to master. There are hundreds of simple frameworks you can start with. Grab any of them, find a simple tutorial and start tooling around.
The concept is simple: send and load information without refreshing the webpage. You'll use the same back-end technology. You'll use a smattering of Javascript for the browser. And you'll be in business!
The problem though is that AJAX app development is a mess (e.g., in terms of dealing with compatibility issues across browsers and different versions of the same browser, using the slow minimal dynamic language Javascript, poor tool support, etc). At least Google's GWT tries to clean up a bit of this mess. A better way to go in the future might be to use Silverlight.
The concept is simple: send and load information without refreshing the webpage. You'll use the same back-end technology. You'll use a smattering of Javascript for the browser. And you'll be in business!