the policy is that students who live in halls have to sign a form declaring that they will not bring a car. there is very little car parking space in oxford, especially near the universities (which have tiny car parks).
also, a lot of the backstreets are permit parking only - i dont think you can be in halls and get a parking permit from the council - which means you will definately get clamped/fined for leaving your car nearby.
fortunately, brookes-town/clubs/pubs is within walking distance, and buses are incredibly regular in oxford (every 5 mins really). when you get there you will see thousands of bikes locked to everything in sight - that tends to be the main alternative to buses. oxford is really ****ty for cars