As anyone who starts using Office 2007 likely knows, one of the more dramatic changes is the elimination of traditional menus and toolbars. These have been replaced with what Office calls the Ribbon. The short explanation of this new user interface is that more commands are displayed at a time without having to hunt through various submenus, dialogs and toolbars.
While the Office team has done work to try and support Office 2003 hotkeys through a method that let’s you type those keys and have them still work, commands themselves have been completely rearranged. For example if I remember that in Office 2003 the hotkey sequence to bring up the Paragraph Format dialog was alt+o,p, I can still press this sequence. However if I only remember that a particular feature I use was located on a certain menu, then it is a bit of an exploration expedition to find the new location.
The Office Online pages have some very handy documents to assist with this challenge. For each Office 2007 application that had an Office 2003 equivalent, there is an article explaining the new UI. Better yet each article has a link to an Excel workbook that lists each menu and toolbar from the Office 2003 version of the program and explains where to find the equivalent command in Office 2007. My Paragraph Format command for example can now be found on the ribbon under Home | Paragraph | Dialog Box Launcher.
Here are links to the articles and the Excel workbooks for the three Office programs I use the most, Word, Excel and PowerPoint.