Disable parent window on Popup Silverlight 2.0

Question

Hi,

I have created a Usercontrol which will be displayed as Modalpopup over the parent window. I have used semitransparent to lock the full screen and then displaying a popup messagebox or control (whatever) on the rectangle.This works fine like ModalPopup or childWindow popup. Problem is when modalpopup is up and if user clicks "Tab" then the tab change happens on the parent window (which is behind the semitransparent rectangle) and not in the popup window. Basically tab changes are still on parent window and not on Popup window. I tried Me.Focus on Modalpopup but that doesnot work.

Is there any best way to overcome this issue. Please advise.

Thanks
Sai