Am I right in thinking this?

All the Behaviors in Dreamweaver add JavaScript to HTML. And Internet Explorer blocks the download of JavaScript. And you have to 'Allow Blocked Content' to run pages with JavaScript. And this is a really bad way to go about designing websites because people would rather not be downloading active script.

Thanks in advance for your comments.

You're right, it's not a good way to go anymore. The old DW behaviors use..well, old javascript. It would be better to look for newer methods using unobtrusive javascript that will NOT trigger the blocked content beast, or forgo JS completely. There are many methods to achieve image rollovers and such these days that don't require any JS.