What type of camcorder are you using? Is it analog or are you recording to DV or some other digital format. How are you transfering the video to your computer? Firewire, USB, or some digital memory card? Or an analog method like component or composite video cable?
And define "pixely". Large blocky effects could be macroblocking- indicating either a playback problem or an encoding problem. However, a playback problem would usually involve both video and audio.
First guess would be some kind of analog interference if you aren't recording digitally. Second and third guesses would be a problem with the encoding or a problem with the camera itself. But more info will help narrow it down.