Practice in front of a live audience... even if just your roommates. Videotape yourself presenting and watch it (painful). I just put some points on presentation materials at http://academicvc.blogspot.com/2008/04/raising-capital-part-... and that might be interesting. Try to have a chance to test out the technology the night before... I know you use a Mac, so that eliminates a bunch of potential failure modes, but still..