I’ll start by saying I don’t have an answer to your original question, but I’m not really sure why you’d need to ask it.
We should be designing for 1024px screens (which the iPad is).
Designing for 1024 does NOT mean having a width of 1024px as jamy_za mentions above. You should be in the range of about 960-980px. This will make sure there is no horizontal scroll (again, like jamy_za mentions he has).