Don't Open That Window

If you're using Internet Explorer 7, there's a way to control how many windows you open.

Go into Tools > Internet Options > General. Underneath Tabs, click the Settings button. In the Tabbed Browsing Settings dialog box, select "A new tab in the current window." Changing this setting instructs IE7 to open a website in a new tab, not a new window, when you click a link in an email message or whatever.