web video slow and jerky

Do you have a fast enough internet connection? Do you gave a fast enough wireless connection?

If you download the whole video yo your hard drive is it still slow and jerky? If not the problem is either a network connection or your wireless csrd

plays fine from my hard drive...   I have fios service.   desktop where problem exists (winxp pro) is hard wired..   I tried it on my notebook - same home fios but via wireless and it is not jerky....

It sounds like there is a speed difficulty someplace in your download. In a typical installation the video will start to show on monitor as soon as the file starts to arrive. If the arrival speed is too slow, the picture will pause until the download catches up with the display. That is why the above suggestions to measure the speed are so important in locating the problem.
A quick fix is to let the file download, jerks and all, then run the file again. It should be smooth the second time.

Probably a slow or busy pipe.  I usually wait for the download to finish.  Then, play it - it plays from the temps on your hard disk much faster.

Your Flash Player up to date?

https://support.google.com/youtube/answer/78358?hl=en

See this link:
http://support.microsoft.com/kb/2532294

Run “Fix it” and check if you’re able to get the issue fixed.
http://support.microsoft.com/gp/video_freezes_or_crashes

Go here in Internet Explorer and update Adobe Flash Player:
http://get.adobe.com/flashplayer/

Now temporarily force Google Chrome to use the "System" Adobe Flash Player rather than its own built-in "Pepper Flash player" and see if that improves things.

Instructions here:
http://helpx.adobe.com/flash-player/kb/flash-player-google-chrome.html
Make sure you use the "release version of Flash Player" when you get to the link.  It should resolve to this URL:
http://get.adobe.com/flashplayer/?fpchrome