Go to the material room and make a new node by right-clicking. Select Create New Node>2D Texture>Image_Map When the new node appears, select the top field (image file I think it is) and then browse for your image. Next, link it to the diffuse root node. If it's a swatch, you'll want to tile it. Adjust the U and V scales to determine the frequency at which it tiles. Once it looks ok in the preview, do a quick render to check it out. I'll post a screen shot in a few minutes, but I'm currently rendering an animation, so it could be a bit.