You're not likely to get questions like "why oxford" or "why law", apart from as starter questions designed to ease you into the interview. The interview is purely academic.
I think it really depends on the format of the interview. Which college have you been assigned to? Quite a few base their interviews purely on material given to students at the interview (typically, it's an extract of a case, and you'll be quizzed on your understanding of that case only) - mine certainly doesn't care for your PS at all. That said, I've heard of at least one which asks more general "
jurisprudency" questions, but in any case, I don't think you're expected to know an awful lot. You're really there to show how you think, and how quickly you learn and process new information. The content will be taught during the course itself anyway.
Depending on what format your college uses, I would suggest getting on BAILLI (
http://www.bailii.org/) and
http://www.legislation.gov.uk/ Have a look at a case like R v Miller [1983] 2 AC 161, read the full judgment and relevant statutes, and see if you can make sense of it. You can pick random cases off sixth form law or e law resources to start.
Ummm I certainly knew nothing about Hart, Finnis, Rawls, Dworkin before my interview; I don't think I even knew who these people were (ironic, considering that Hart is from my college). Actually, I'm not sure I understand them now even after graduating with 2 law degrees, but I suppose it doesn't matter.
It's true that Oxford makes Jurisprudence compulsory (notwithstanding the multiple attempts made to make it non-compulsory within the faculty), and they do ask students to consider the theoretical fundamentals in every course (to some degree). That said, familiarity with legal theory is
NOT a requirement for admission. My own college certainly doesn't base interviews around legal theory - the tutors just give you a case extract and ask your questions about it. It's more oral comprehension (understand +
apply the principles derived from the case to novel fact patterns) than critical analysis (which would be something like "Do you think people should be criminally liable for omissions?"
Can confirm the Stanford philosophy encyclopedia is pretty handy though.