Flash is completely different than AJAX and believe me if you aren't a designer then don't go for Flash (Actionscript). Ajax give you power of server side coding staying on same page, mean you don't have to refresh page (Contact server) to fulfill a request. Using Javascript and XML calls you can perform the same thing which will be displayed after page refresh. Many people are describing AJAX as a tool which helps in solving the problem of page refresh but its not true.

If you are new to AJAX world then various frameworks are available check the list

These tools will definitely help.

AJAX must be used very carefully as there are few disadvantages of it. Read this article

Overall, AJAX is a great platform for web developers. I would suggest use a framework (ExtJS or MooTools) and you are bang on!.

I hope it helps. Your comments are welcome.