Hello, This is a problem a lot of people might have when playing digtal video with Windows Media Player. The quality might be worse when viewing in media player than in Vegas Video once you have rendered to a DV-AVI or other file. That's because there is a quality setting in Windows Media Player that is quite hard to find. You have to go in the "Tools" menu and then in the "Options" menu. Once you're there, select the "Performance" tab which is to the right. You will see an "Advanced" button in the bottom, click on it and now you will see a slider that goes from "small" to "large" and which is labeled "Digital Video". By default it is about 3/4 from the begining, meaning video won't playback at it's maximum resolution. Just move the slider to the right and you will see great improvment in quality, it'll be the same quality than in Vegas.
Hope this can help some !