How intense of 3D modeling? Just basic geometry, or fully rendered scenes? I would say get a relatively fast processor, with a decent sized memory. It can take some time to apply layers in image programs, expecially if they are complicated, so you'd need the memory there, and the processor will help when converting file types. Now, you'd need a GPU with good technology (not necessarily speed) to render a scene with realistic detail. Go check out the new Nvidia GeForce 7800 GTX. It has some amazing technology built in.