While writing my software rasterizer for the GP2X (which does not support floating point arithmetic in hardware) i developed a small fixed point math library.
The library consists of various functions for dealing with fixed point numbers (multiplication, division, inversion, sin, cos, sqrt, rsqrt). It also contains a C++ wrapper class which can be used to simplify working with fixed points numbers greatly. I used this fixed point number class in conjunction with my vector_math library to obtain a fixed point vector math library. Doing so made the 3D computations a lot faster compared to the floating point version.
You can download the source below: