This may not be a complete answer to your question, but keep in mind that a lot of the pictures you see posted here do not come straight out of a Poser render, but have a lot of detail and touch-up added afterwards in PhotoShop or another graphics program.

Also keep in mind that no matter how big you make the picture in PhotoShop, you are constrained by that with which you originally start. For the detail to really appear, you need to initially draw it at high resolution, or scan it at high resolution from a high-resolution source. You will also need to render it at a high resolution to capture it (render in a new window, perhaps at much higher resolution than what you intend for your final product).