Susan,
When you say you have to download Ajax... do you mean Spry Ajax Framework? Ajax, alone, is not something that you would download but rather a protocol of language using javascript and server side code.
It may be that you need the latest Adobe Spry Framework for your Dreamweaver... if that is the case, click here: home.html
You will need to sign up for an Adobe username is you don't have one already... but just click the download button in the upper right corner, unpack and install it. It will install automatically to your Dreamweaver installation.
Cheers,
Brian
