How an Ortho W-Friendly Projection Matrix must look???

Hi:

When I activate a W Buffer with a GeForce using a perspective projection matrix the results I get reading W buffer are OK, but in the case of Orthogonal projection it fails. I am afraid that it is due to the fact that my ortho projection matrix is not compliant but I can not find How an Ortho W-Friendly Projection Matrix must look.

Thanks in advance