Thank you for posting to the NI forums. After doing a simple V=IR calculation using 5V and 700 ohms, the current requirement is around 7mA. The specifications of the PCI-6503 specify that the card can only output 2.5mA. Trying to do anything above that could damage the card.
Is there anyway that you could up the impedance of your device? You may want to consider an external resistor or the PCI-6509.
If you are able to increase the impedance of your device to account for the 2.5mA, then I would point you to the examples that are shipped with LabVIEW. You can access them by opening LabVIEW and clicking on Help>>Find Examples. This will open the Example Finder. Double click on Hardware Input and Output>>DAQmx>>Digital Generation. This will lead you to a list of examples. You can view a description of each example on the right hand side of the screen by clicking on an example. I would recommend the Write Dig Chan.vi as a starting point. By opening Measurement and Automation Explorer (Start>>Programs>>National Instruments>>Measurement and Automation Explorer) you can determine the device number associated with your PCI-6503. The device will be listed with a device number under My System>>Devices and Interfaces>>NI-DAQmx Devices on the menu tree on the left side of the screen. You will use this device number to pick your device on the front panel of the example vi.