Hi Pixie,
Mine's Tuesday, so I'm starting to feel as you do. I have to give a 30 minute presentation followed by an hour of questioning - sounds like fun!
The only advice I can think of is to know your stuff, & I know that sounds lame & obvious but it's easy to forget that you're the expert here - you know what you've looked at & why, & where you're currently working, better than any of the panel.
Mine is broken into 5 key areas I have to prove, & I'm probably saying what you already know, but they are
1) The research problem: 2) related literature: 3) appropriate method: 4) realistic schedule & 5) original contribution to knowledge, so I've planned my presentation around those.
Otherwise, don't forget to breathe - out as well as in, I always forget the exhalation bit when I'm nervous!!
Good luck & let us know how it goes, Mog (up)