Where are the unanswered posts? It looks like this is your first and only post on these forums, at least with this user name, n'est ce pas?
While I am not PMDX, I try to lend a hand when I can. There are several (many?) threads here about people running PWM on a PMDX-126, and I had it working on my board, back when I used a PMDX-126. Granted, not to a laser, but to a PMDX-107.
Perhaps if you can tell us about your setup, someone here might be able to help. For example, Mach3/Mach4? Parallel port, SmoothStepper (I may not be much help here), PMDX SmartBob or other interface to the PMDX-126? What signals does your laser controller need, and what voltage levels? How do you have the PMDX-126 wired to your laser controller? What is your Mach3/Mach4 configuration? What commands are you using in Mach to turn on the PWM? What behavior do you see on the PMDX-126 LEDs? Stuff like that.