perspective projection

i wanted to display a cube in perspective projection. i wanted to do all the calculations for the perspective projection without using the in-built funtions.
the vertices of the cube are:
0 0 20
10 0 20
10 10 20
0 10 20
0 0 50
10 0 50
10 10 50
0 10 50

as opengl has screen size ranging from -1.0 to 1.0
i would like to know wut should be my world co-ordinates maximum and minimum values, how to define the frustum, where to place the eye so that the cube would be visible…and i just want my algorithm to be generalized for any object…i would also like to know about the camera direction and also placing the camera…i never used opengl and i’m new to graphics…i would appreciate if someone could help me…

tutorial 1 to 3 …

thanx i got some idea from this