How long does windows wait before deciding a window is unresponsive and brings up the the unresponsive chrome? Just from anecodotal experience, I assume it is different in XP and Vista, as they are handled very differently by the DWM in Vista and the Explorer shell in XP.
Taken from Windows Error Reporting at MSDN
An application is considered unresponsive (or hung) if it does not respond to Windows messages for five seconds and the user is trying to interact with the application.