Prolly the easiest way to improve sound is to use an external recording device like the Zoom H1 and synchronize the .WAV file in a video editor by using a hand clap with both devices running. In the editor the hand clap will be visible in the video, and in the added .wav file the clap will show up as a spike on the sound track. Synchronize the 2 and then disable sound on the video track; now render video from a point beyond the hand clap. Video editors can be had for free and the Zoom H1 is prolly the best bang for buck. You can also run a cable from the Zoom H1 to the Camera's Mic input if it has one. Good luck!