How to centralize an event handler for all the workbooks that are open ?

In other words I want to handle cell click event from workbook1.sheet1 in to
an addin (say HandleEvent.xla).

In the similar fashion I want to create a tool bar from this addin, only if
a specific workbook is opened.

( I remember using Public withevents oExcel as Excel.application to get a
handle to any workbook being opened from a centralize addin. But can not
recall any furthur)

Any ideas???

Thanks in advance

Nayan