Well, it's quite easy if you're using Premiere or probably any quite good editing software,
In premiere import your music file first, then use the "+" key, or the zoom-view slider to zoom in on the timeline, then expand your audio layer using the little down arrow on the left hand side of the timeline, then you'll see the wave-form of the audio, so it'll be easy to see where the beats of the music happen.
Then move along the timeline until you get to the right beat and right-click and select "set clip marker" or something like that and it will put a little marker where you need to edit the video to. You can do the same to put clip markers on the video, then drag the clip by the marker until it snaps onto the same place as the audio marker.

For the clip linked-to above I just zoomed the timeline a lot and used trial and error to get the positioning right because I was using Pinnacle 7.

There's another thread about this in the Premiere part of the forum but I couldn't find it when I looked just now, I think it just says what I did though. good luck

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