Funnily enough, that was what another member was trying to argue with me (no! I mean discus) recently.
But it's wrong. CPU speed does far more than give jerky images. Ditto the RAM.
Tecchie session coming up. Look away if you are easily bored....
When SS08 creates an image, it doesn't draw a picture. What it does is to send a set of instructions to the Windows video sub system. That uses the video drivers and a load of other gubbins to produce the set of instructions to the card which tells it how to draw the image, item by item on a layered basis.
So it takes a finite amount of time to send all of the instructions on how to draw each image (each "frame"). If, in the meanwhile, the card receives the "draw that picture NOW" instruction - dictated by the refresh rate - it will draw whatever it has produced so far. Anything it hasn't drawn is dropped. That's why low-spec systems loose details and parts of Titanic etc (or the entire thing).
If it hasn't drawn enough of the image, the card may simply repeat the last good frame - hence low FPS or jerky images, while the same one gets repeated.
More RAM means that Windows can write it directly to memory without moving other stuff out of the way. So less RAM means that Windows is distracted from the task in hand. So details go missing and you may get jerky images, etc.
A slower CPU will cause exactly the same effects.
On the other hand, a Video card which is below spec can fail to accept the instructions from Windows fast enough. Same thing - missing frames, details missing etc. Some older cards may not be able to carry out the instructions that it receives ("Shader" problems are common with SS08 updates. Some older cards can't understand those instructions). In this case, whole segments may be missing, or odd textures may appear (like a white sea or lattice-work waves and so on).
Similarly, the video driver may not be optimised to rapidly process and convert the instructions from the video sub system. Or may not be able to process certain instructions. Same things as before, i.e. missing details, jerky images and so on.
5 minute guide completed. Hope it's of some use.