If you are using Office 2007, but are frustrated when you can't find the features, Microsoft has released an animated interactive command reference tool. This tool can be viewed through your web browser (just set a bookmark), or can be downloaded to your computer. Full text for more.
This tool basically allows you to navigate to a menu item using the Office 2003 menu structure, and then the tool will show you where the same feature is inside of Office 2007.
For example, if you know how to insert a Pivot Table in Excel 2003, you would just navigate to the 2003 menu item as in the screen shot below:

Then, after you click the menu item, the Interactive Command Reference will show you where that same menu item is in the new version, as seen in the screen shot below:

The link to the Office 2007 Interactive Command Reference is: http://office.microsoft.com/en-us/excel/HA101491511033.aspx