Don't tell people what to do, they don't like it.
Do you really think someone is going to go download the latest version of MSIE or Netscape just to see your page? Do you think they are going to go download Shockwave so they can see your product ads? Pretty conceited of you. Unless you happen to be Microsoft or Netscape, forget it. If you aren't running a site full of Shockwave demos, forget it They are not going to even change page width for you. They have the page width set where they like it already.
Live with it. The web is what it is. People are not going to change their ways to please you. If you are running a company intranet, you can get away with having everyone use the same browser and plugins, but even then, some are probably going to put the screen size where they prefer it. And there is no way you can control the whole web. So make your pages adaptable. Don't put up non-scrolling frames. Don't put up absolute size anything, including tables and page widths, unles you have a darned good reason. Let the browsers do what they do best, which is to make things readable for anyone anywhere.
I can hear the objections already. "But it doesn't look right if..." Again I say, live with it. The web is not television, the web is not a magazine. The web is the web, something new, something different, something you cannot absolutely control. If you do your pages in well written HTML and CSS, and put in the fancy stuff in such a way that it doesn't hurt the site for people don't have the same browser or the plugin, your page will look good to everyone. It may not look "right" by your taste, but it will look fine to the majority of the people who see it.
If you want to use Shockwave, or other plugins, no problem. Just don't try to tell people they must have it to see your site. Say something like "this section requires Shockwave, you can download it here". And don't require the plugin on your important pages. If you treat people like they are there for your convenience, I promise they won't return.