[Hampshire] Video problems with virtualbox

I have virtualbox running successfully on Ubuntu 10.04 on both a desktop
and a laptop. I use it to run Windows 2000 in a virtual machine.

However when trying this on a third PC there is a slight jittering on
the display most noticeable in lines of text. I have installed the guest
additions.

I have tried changing video resolutions within Win2k but there is no
improvement.

I couldn't find anything in the virtualbox forums or general searching.

Roger