Find out the analog output specs on your EMG amplifier. It is probably something like +/-5V. Set up your DAQ card input configuration to NRSE mode (non-referenced, single ended) and set the input range to something that matches or is greater than the output range of your EMG amplifier to prevent clipping your EMG signal (it is unlikely that any damage will occur even if it does clip). Wire the ground/common from your EMG amplifier to the AI-SENSE input and the EMG signal output to one of the analog inputs (i.e., AI0).
Regarding safety, the EMG amplifier should provide some safety in the form of fault current limiting or galvanic isolation from the electrode inputs to the power supply, ground, and analog output. For increased safety, run the PC on batteries (not connected to the AC mains) or use a medical-grade AC isolation transformer between the AC mains and the PC. As always, consult with a qualified biomedical engineer to inspect the system before connecting it to humans.
Also - please see our Biomedical User Group at www.ni.com/biomedusers - there is a wealth of information here, including information on the free NI Biomedical Starter Kit, which includes VI's and mini-apps for data logging and signal processsing of ECG, EMG, and other tools.
