What is the Ribbon in Office 2007

The Ribbon replaces the current system of layered menus, toolbars, and task panes with a simpler system of interfaces optimized for efficiency and discoverability.

The 2007 release of Office provides two ways to customize the RibbonX UI using XML markup:
Using valid Open XML Formats files that contain XML markup. Using COM add-ins that contain XML markup.

One of the nice article i gone through in the MSDN is ...

Code:
public void OnActionCallback(Office.IRibbonControl control, bool isPressed)
{
if (control.Id == "checkBox1")
{
MessageBox.Show("You clicked " + control.Id);
}
else
{
MessageBox.Show("You clicked a different control.");
}
}

using VSTO for visual studio 2005 we do these kind of C# coding in ribbon or add-on development for office 2007.