If both your main router and one of the spares supports WDS you could do this wirelessly.
Otherwise you will have to link the two via ethernet -- which would extend your wireless range in the rather clumsy fashion illustrated here:
See link:http://kb.netgear.com/app/answers/detail/a_id/965
I'm not familiar with how DVR's normally work but as an example of using spare wireless routers to bridge a gap in wireless coverage I do the following:
Laptop in top room is used for scanning images which I need to e-mail. Laptop is too far from main wireless router. Add spare router to laptop. Retrieve files from laptop using wireless adapter in nearby desktop that is within range of main router.