The quality has nothing to do with the video playing like that on your computer. Somethin in your computer is taking up too much memory causing the video to lag. I used to have this same problem back on some old shitty pc. Best thing to do is close all the programs and like Farzin said, download up to date codecs along with the divx codec. If that doesn't fix it then something is wrong with the computer. The quality of the video has nothing to do with it lagging on your computer.
It doesn't help that he is running Windows 98.
Well fuck there's your problem hahaha