Answering your first question, I will strongly suggest changing drivers, instead of using the traditional DAQ drivers use the DAQmx drivers, and it sound like you are in a staring stage position so DAQmx will make your programming a lot easier. This document: Data Acquisition (DAQ) Installation/Configuration will show you that the PCI-6503 is compatible with DAQmx.
To setup your device in either direction you choose to follow, DAQ Getting Started Guide will guide you through the installation of the software and the hardware.
Regarding your second question since you want to use the card to drive a relay, I have to suggestions for you in DAQmx, you can use the: “Write Dig Chan.vi” example, located in Help->find examples->search tab and type the name of the example. For a Traditional set of examples you can open any of these libraries as a guide: “C:\Program Files\National Instruments\LabVIEW x.x\examples\daq\digital”, the one I will suggest to look at is: “C:\Program Files\National Instruments\LabVIEW 8.5\examples\daq\digital\653x.llb” Write to 1 Digital Line.
I hope it helps