If you can't see the ExitReality button (which looks like a dark ball with an orange X cut into it) then it is most probably covered up by other buttons on your IE7 toolbar. The givaway for this is the presence of small arrows on your toolbar. They look like this: >>

Click on these and you will most likely see the ExitReality button.

You can also right-click on the toolbar and select Customize Command Bar >> Add or Remove Commands ... which will bring up a window where you can move your toolbar buttons around, delete buttons you don't use etc.