How should I prepare for my Computer Science and Philosophy interview? :)

I'm a little nervous as I haven't studied either of these subjects in school - except Comp Sci at GCSE level years ago.
I assume that I'll have separate interviews for each subject?
Any help would be amazing

I'm a little nervous as I haven't studied either of these subjects in school - except Comp Sci at GCSE level years ago.
I assume that I'll have separate interviews for each subject?
Any help would be amazing

Yes, you'd normally have separate CS and Philosophy interviews, although this may not always be the case, because both subjects are essentially looking for similar logical reasoning skills. (With a slightly more numerical focus for CS, and more verbal for Philosophy.)

For CS there is some helpful information on the official website:
http://www.cs.ox.ac.uk/admissions/undergraduate/how_to_apply/interviews.html
http://www.cs.ox.ac.uk/admissions/undergraduate/how_to_apply/sample_interview_problems.html
http://www.cs.ox.ac.uk/admissions/undergraduate/how_to_apply/interview_sample.html

For Philosophy, make sure you're happy to talk about anything you mentioned on your personal statement. But beyond that, it's difficult to see how you can prepare. Part of the point is that they'll throw some things at you that you've never thought about before.

I can only offer general advice as I interviewed for History
Making sure you've re-read things mentioned in your PS and go over the general/specific theories of each subject/what's got you interested in them despite studying so little of them at school would be a start.
The interview is mainly about seeing how you respond to deep, specific questions about your subject as well as testing your ability to adapt your answer when new concepts and information are introduced, so thinking outside the box. As long as you've got the foundations covered, don't become too stressed about the interview.
Hope that somewhat helps

Thank you for your help I'll just reread my personal statement and read some interesting books in the meantime then. Honestly, I'm quite excited now!

How many interviews do you think I'll have?

Hmm could be any number really. You'll have at least two at your first choice college and probably two at a second college. And then sometimes people have more. Or you might have less (I only had one at another college).