Look at old 3d/game programming books and tutorials, stuff from the dos area. You'll need to write your own rasterizing routines and the old techniques are still valid, one thing that has changed is that you no longer have to deal with colour lookup tables and quantification.
Yeah, Irrlicht has a software renderer. Though it's slow as hell and most functions don't work (it can't handle much more than rendering a model and some GUI). But that's why it is a software renderer of course .