I use a casio dig camera that happens to take decent videos too.
on some cams there is a volume setting for the mic, but be careful of noise. One recorded though there is audio and video software that you can use to edit the sound quailty. I am using Goldwave for the audio and Sony Platnium dfor vidio but there are free options too like Audacity and Windows movie maker.
for the audio if the cam is all you have and you have no computer skills or dont want to mess with that, you can try some of the tricks used in the good old days of sound and video production. Study some of the pioneers in film and what they did.
One of these tricks was recodign in a tiled bathroom, the very 'live' ambiance of them, and the reflective surfaces creates a lot of natural volume and echo to be returned to the mike. You could try a public bathroom, if you dont have that, clear out a corner of a room and perform in that with bare walls, a totaly bare large room is better. but experiment with camera placement because with that much reflection you can get what is known as 'cancelation' where sound waves meet and cut out certain frequencies , which will alter your sound for better or worse depending on your mic. I hope these tips help good luck with your video.
