To tile a texture in Poser 5, you have to make a few adjustments in the Material Room.

Find the material you want to tile. The 2D image node that loads the texture has a couple of channels called U_Scale and V_Scale. Change these values to make the texture repeat itself. The default value is 1.0 (no tiling).

Note that the real-time preview in the document window probably won't show the results of your changes. You'll have to render the image to see the tiled effect.