[setishock]

Stylevars > Common > Doc_background
As for jerky several things can come in to play.
Slow connection on the member end. DSL is ok if you're the only person on it. And a lot of forums like mine are not dial up friendly.
Slow computer and or built in video chip on the member end. Can't render the image fast enough. Also here if your image is large as in byte count it can slow down the page being rendered when you scroll the forum. You can wash the image through a digital enhancer program and reduce the image quality to say 50% to lighten up on the size(byte wise) of the image.
Too much going on. Too much java and or flash will slow down page loads and refreshing by the browser.

Since you say you have "some" members having problems, the starting point in trouble shooting is "them". Find out what computer system they have. Ask for type and if the video is built in or a card. If built in tell them to kick up the shared memory and see if that helps. Ask what type of connection they have. Are they sharing it? Does it do it all the time or when little Billy is online playing games or sis is facebooking.
Two favors to ask. 1 Next time post a link to your forum. 2 Come back and let us know what you found out.