I think the passport will automatically get you in to the German stream and may give you priority (first on the list if space available) for the international, but please confirm this directly with the school. I can't remember exactly what they said when I visited. You should ask how long the wait list is for places and ask for an honest assessment of whether your kid has a chance, assuming they pass the assessment.
We interviewed there but choose HKIS instead primarily due to facilities, Mandarin language instruction, location and a desire for a more US-based education rather than a European one.
As your child is still young and most schools don't start until four not getting in this year really isn't that big of a deal. There are plenty of private kindergartens all over HK you can attend such as Woodlands and Tutor Time. Come September you can apply for 4 year old places at most schools as part of the regular admissions process for 2012-13.