Are you playing in movie maker, or are you exporting then reviewing the exported footage?
If the first answer is yes, you may simply be importing it at smaller resolutions or perhaps have it on a "preview" setting that allow faster playback at the expense of quality. Look at your project settings and check the resolution and quality vs what you're importing.
If the second answer is yes, then you may simply be exporting at undesirable settings, making the final product really ugly. Try different export settings, keeping an eye on resolution as well as the quality settings for the video format (.WMV I assume?).
