Unlike Firefox, IE7 does not offer a command that allows you to reopen recently closed browser tabs. But there's an extension you can load for IE7 called "Open Last Closed Tab" (it's not going to win any prizes for creative naming) that allow you to, well, open the last closed tab. Once it is loaded, all you need to do is hit Alt + X in IE7 and it will open a new tab containing the page that you accidentally closed when you closed the tab.