Internet Explorer has certainly come a long way since version 6. IE8 is a big improvement and sport a number of very useful features.
One of those is the ability to access more than one CM account (or any other account that utilizes sessions). Head to the file menu and click New Session and IE8 will spawn a new window that doesn't share session information with the original window.
To launch a new window from a shortcut, just add the -nomerge parameter to the end of the target on its properties page. Double click it, and the new window will open free of any baggage from previously launched instances of IE.