It's possible to do a realistic render in any program- radiosity isn't necessary, and most procedural effects can be faked in Photoshop within a few hours. The main trick is getting the textures right, closely followed by hi-detailing the models (even non-organics often benefit from some subdividing, etc.). I've never seen lights as all that important, but soft shadows and radiosity are nice when you can get them. But by far the hardest bit is textures. A model you can generally tell what's wrong, and there's usually a simple solution- a texture has to look exactly like it does in life, or it just won't look right. Your best bet is to have a picture of the texture type you want handy, and base a procedural (no mapping, and thus better) off that (like one does with a complex from-life model). Use a color picker to get the predominant colors off the picture, for one thing.