you'd get the best quality if you used a digital camera as a webcam... rather than an actual webcam. Most normal webcams only capture at a resolution of 640x480... which isnt too great.
You have to remember that if you're broadcasting this webcam over the net then it will be compressed and things like signal noise and data corruption will greatly affect the quality anyway, so sometime having a massivley great webcam doesn't help at all
dragon2309