http://mysbfiles.stonybrook.edu/~reick/dots.swf
I finally beat it again today, not counting this past week I haven't played this since senior year of high school.
Normal: Dots go left/right and up/down at the same speed.
Medium: Dots go left/right and up/down at different speeds.
Hard: Dots go left, right, up, and down at different speeds. Once they reach the end of one side they start from the end of the other.