If your users find aero preview annoying, you can disable it for them by enabling the following Group policy setting:
User Configuration/Administrative Templates/Start Menu and Taskbar/Turn off Taskbar Thumbnails
If they only find it annoying for Internet Explorer, you can disable it for IE only by clearing the "Show previews for individual tabs in the taskbar" checkbox on the Tabbed Browsing Settings, which can be accessed from the General tab of the Internet Options dialog.
Mitch Tulloch is a seven-time recipient of the Microsoft Most Valuable Professional (MVP) award and widely recognized expert on Windows administration, deployment and virtualization. For more tips by Mitch you can follow him on Twitter or friend him on Facebook.