I would say that the main things they are looking for are:
have you read enough about your subject to understand where the gap in knowledge is that you research will fill?
have you got well structured research questions that you can answer?
have you got a workable methodology?
have you got enthusiasm for the subject that will see you through?
have you got a timeline that shows your phd can be done on time?
So your presentation needs to show on some level that the answer to each of the above is yes. Be clear where your questions have come from, drop in key authors etc, be clear on what you are doing and how, be clear on what you will be doing in your 1st, 2nd and 3rd years. Overall, be enthusiastic about your subject as this will reassure them that you can keep with it.
Best of luck with it :-)