Well, generally speaking, preloading images for table view is a bad idea. Think of a following situation: you have 100 cells, each containing one image. That means you'll have to load 100 images before showing the table, which will have a serious impact on avaliable memory.
The "loading effect" you're talking about can be caused by two things:
a) as you have said, the problem with loading images. If so, do it in another thread, and pass the image to main thread when it loads
b) You're using images that are bigger or smaller than the given size. This will result in resizing the image when it appears on screen, causing the ugly stop-effect - the solution is to draw images in size which is exactly the same as their size.
Chope this was helpful, Paul