Scully has given you some really great suggestions - I've given lectures to a number of audiences over the years (undergrads to senior management & government officals) and have found that "distractions" like Powerpoint or a movie etc are really useful, especially if you feel self-conscious - you can turn the lights down (not off!) and this can help you to get over the feeling of being in the spotlight with all eyes on you. Also consider getting a remote controller for the PC - I've got a Logitech R-RB5 that is designed to work with Powerpoint - as this allows you to move around the room & not be tied to the mouse (or have to run back to it). It is worth its weight in gold. Also make sure that your presentation & materials are on the PC - not a network - as I have had the experience of losing network access (and the presentation) - and have had to run "dry"
Flip charts can be useful, but you need to feel in control of your subject to use these effectively.
Yes, humour does work, but in carefully judged quantities and appropriate to the subject matter. Also consider using handouts etc.
Hope that this helps