One of the latest feature in the Internet Explorer 8 is to login to the same site with multiple accounts simultaneously. Using this feature you will be able to check mails of two Gmail or any other webmail accounts while running only one browser.
Its a simple task to use this feature. Click on File in the menu bar then select New Session. If menu bar is hidden then press Alt key to view it temporarily. After selecting New Session a new window will open. You can login in to the same site in this new window.
Quickie: If you are going to use this feature regularly then, you can create a shortcut to IE8 with the paramater -nomerge. This will have the same effect as selecting New Session from File Menu.