Of course, if you're using Firefox 1.0, there's a way around this:
1. Enter about:config into the location/address bar.
2. Right click in the list of preferences and choose New | Integer
3. For the preference name, enter: privacy.popups.disable_from_plugins
4. Set the value of this to "2"
5. Close the window.
This will prevent plugins from opening new popup windows. Of course, there may be unforseen problems to this solution, (like, plugins that legitimately need to open popup windows)