How to activate a custom ribbon tab

[wmbb]

I've created a custom ribbon tab using the Custom UI Editor For Microsoft Office.
The tabID = "tab1".
I want to activate this tab on opening the document in WORD 2010.

I found some code but I dont know how to use it...

Public myRibbon As IRibbonUI

Sub tabActivate(ByVal control As IRibbonControl)
   myRibbon.ActivateTab (control.ID)
End Sub

The code below doesn't work.

Public myRibbon As IRibbonUI

Sub document_open()
  myRibbon.ActivateTab ("tab1")
End Sub

Can somebody help me with the code...