I've never used a NightOwl model, but based on the other DVRs that I have used, it's generally an IP address with a port number associated. What that IP address is, depends. It could be set to DHCP, which would be given an address by your network (router). Generally, best practice for access is to set the address manually, so you always know what it is, and can setup things such as port forwarding.
Having said that, I believe you will need to connect it to a TV or monitor to access and change these settings directly.
The only other way, is if you have (or find the manual) and it's set to a 192.168.x.x address by default. Which you could then set your computer on an address on that scheme, access the DVR, and change it (if the capability is enabled via remote access).