Hi labview1958,
DAQ 7.1 has support for LV6, so there shouldn't be any problem. Since you're using the Traditional DAQ driver, there should be very little changes from the driver you're currently using. This driver should automatically overwrite your existing driver, since there's no need to worry about corruption.
Duty cycle is the ratio of the duration (time) that a signal is "ON", to the total period of the signal, while pulse rate usually refers to the signal frequency, and period is the inverse of the frequency, hence they are not equivalent to duty cycle. I'm not able to see the VI from the attached document, but there should be another parameter that will allow you to control the duty cycle.
The pulse train output will be TTL logic, hence it will go from 0V to 5V. You can use the analog output to produce a square wave, which will give you a range from -10V to 10V (If you're interested in using the analog output, check the Function Generator shipping example). But to obtaine 20V or 40V, you will need some external circuitry to amplify the signal.
Thanks,
Lesley