How can I improve my video quality on YouTube?

Right now I'm using a Cannon PowerShot SD 1300 IS point and shoot camera to make home videos to upload to YouTube. This camera has two video settings: 640x480 30 fps and 320x240 30fps. I use the 640 setting.

When I edit the movie on Windows Movie Maker it looks fine. When I upload to YouTube the quality is significantly diminished.

I am a complete newbie when it comes to this kind of thing. When I publish the video on Windows Movie Maker I always choose "best quality for playback on computer". When I upload to YouTube the color is off, it isn't crisp, and appears poor overall.

I'm willing to invest in a new camera and new editing software if need be. In the meantime why do my videos look bad on YouTube? Is there anything I can do to make my videos look better with this particular camera?

Thanks for any advice.