It's ok: I wrote the wrapper interfacing almost every matrix-related function of OpenGL ES 1.0 in order to keep track of the current matrix state. That was really annoying and stupid to do that, but now it works. Furthermore, I converted everything else to fixed points, but still keeping a full compatibility with my PC engine. I got hardware acceleration, yuppi!
Thanks for your help, especially to drgoldie for the PMs...