Unless you are doing very, very slow PWM, the USB-6008 is not a good device, because it has software timed digital outputs. The maximum output update rate is about 150 Hz. At that rate you are likely to have substantial amounts of timing jitter due to OS latencies.
Unfortunately it is all I have available at this time, yes it is quite slow, somewhere in the region of 4 pulses per minute or 0.07Hz, so I imagine it should be within the capabilities of the USB-6008.
I think there are some examples on PWM. Start by looking at those. You will probably need to make some modifications, because it is likely that all the examples will assume the PWM will be generated on hardware timed DO devices or devices with counters.
