Microsoft has published a list of the changes made to IE in XP Service Pack 2 that may affect probably a lot of web pages.

Web Pages using

• ActiveX controls: the modal dialog will no longer popup automatically. Users must specifically click on the pageholder to install controls
• Downloadable Files: The file download ability can only be initiated by a user click. Pages that say "your download will begin in 10 seconds" and have an ad before launching the file will now fail.
• Popup Windows: These may now only be initiated by a user action, not automatically, and only one popup will be created based on that user action… so a popup cannot spawn a popup, even if the original was spawned by a click.
• MS Java Virtual Machine: This is no longer distributed. You should direct your users to java.sun.com… well – I guess that's the way it's been so far already ?
• Browser Windows Alterations: You can no longer do a fullscreen window, it will only launch a maximized window. You can no longer move the statusbar, titlebar or toolbar off of the visible screen.

should be changed in the future…

Well – as you can imagine – all those changes are against paypal and banking scams, dialers and spam popup-terror – the usual threats for most of the normal windows IE users… and everything already implemented in alternative browsers…

Here is the full article