Ah yeah, there you go, one of the discussion threads. I wasn't sure those forums were still around since libtcod stuff has disappeared before and some of it hasn't returned.
Really no matter what tile solution you use, you're going to end up with multiple layers, at least for the ground and whatever's sitting on top of it at that position (if anything). Unless you go the black background route, which generally calls for simpler tiles. pat's example in that thread looks pretty good, and is fairly simple to implement. That only requires one layer (though he's also demonstrating the use of subtile sizes there, something you don't necessarily need).