handle the onchange event of inbuilt tabs of office2007

Hi

I hv added an addin in Office application (word , excel , powerpoint , outlook)

e.g

open the MS office 2007 word application
there are tabs like HOme , Insert ,Pagelayout views etc
when we select the Home tab then the groups of related to that home tab displays like clipboard , font , paraghraph etc .
In same way i want to change the contenet of my addin when user selects the tab home , insert , view etc

Thanks