Mapping a rectangular texture onto a closed object

Hi all,
I have just started using blender (seems great). I have a procedural texture generator that generates height maps and texture maps that wrap horizontally and vertically. I am now trying to apply the texure to a simple closed object (say a cube).
I am finding this to be very difficult since it inevitably causes seams. I can remove these seams by selecting “sphere” mapping under the texture “map input pannel”, but this causes a singulariy at the top and bottom (as one would expect).
Creating a UV mapping that resolves this also seems to be impossible. The only solution that I can see (as a total newb :o ) is to try and build a texture that is tilable not just horizontally and vertically, but also when rotated by 90 degrees (I have no idea how to do this).
Does anyone have any suggestions? I imagine that taking a repeating texture and tiling it over a closed object is something that is done quite frequently.
Also, if anyone has suggestions for texture synthesizers (specifically ones that also support normal map synthesizing), I would greatly appreciate this.