Need a bit more info... like a picture... but:
1. If you mean the size and placement of everything gets messed up (which is my first guess), it might be that the projector is making your MacBook go into a much lower resolution to mirror the displays. This can be slightly mitigated by going into the display settings in system preferences. Change the resolution. This may vary depending on how you connect to the projector (VGA, DVI, HDMI, etc).
2. If you mean the video is getting distorted, you've got a bigger problem.