Components of a good computer for doing graphics and design

That would depend entirely on what software you're using and your budget!

how demanding is your graphics and design?
maybe you would want some decent gpus..
if you're really seriously professional on this you might want nvidia quadro or ati firepro graphic cards
maybe if you're designing and want just a mainstream card (in which i mean a nvidia geforce or ati radeon hd) you might consider nvidia physx technology which proves very effective.

mi1ez is very right - it all depends on you're program and budget

Depending on what your doing, and your budget, we could recommend from a single budget quad core all the way up to a server board with multiple 6+ core processors.

Heavv Graphics and Design?

CPU: Corei7 based processor
GPU: ATi Radeon 4xxx or 5xxx series GPU (Preferable a 4850 or higher or a 5750 or higher).

Why not nVIDIA? Because the 2D image sharpness and the color reproduction for nVIDIA is subpar at best (not what you want for heavy graphics). Both AMD and Matrox have the best 2D image quality but only AMD has the ability to use GPU acceleration in Photoshop out of the two.

Why a Core i7? Because it will offer you the best performance for demanding Heavy Graphics work. It is 2-3 years ahead (architecture wise) than any other architecture on the market today for such applications.