How to add 6 DOF movement to my engine?

Well I know from many tutorials how to do movement along x and z axis like

xpos -= (float)sin(rotationpiover180);
zpos -= (float)cos(rotation

…but what if we have a descent or forsaken style movement, how can we do movement along x, z and y axis at the same time.

ok i’ve got it… simple mathematics… how could i be so stupid…