I'm guessing I should plan for low resolution and big fonts? Any good examples out there?
If your site has a high contrast accessible version (such as BBC sites do) you could likely use that and the principles they use to design for projectors. Try treating the projector like a user who can't see very well.
- Use a dark background with light text, or a light background with dark text - anything with high contrast
- Use big, bold fonts, preferably sans-serif so there aren't any details that might make the font harder to read
- Zoom in by using CSS rules, or just increasing the size of everything in a separate stylesheet
- Customise the mouse pointer using CSS so it's easier to see when moving around in low contrast. The black cursor on Mac OS X is great for this.
See the BBC's Accessibility guidelines for more info.
If you plan on using soft colors and gradients, consider having a few print outs of the intended color, so that if and when it is rendered horribly, you can show them what it should actually look like.
Edit: Also if you have the luxury of using the projector a few minutes before the presentation, adjust its contrast, brightness and color setting if available, they are usually set to high contrast values.
2nd Edit: After learning this is a site to be mainly used on projectors, I would suggest using black and white, along with 1 bold color, to minimize the amount of poor rendering present.