I've used Belkin in the past but I can't recall the menus and pages from memory, so some of this may be vague. On a Linksys for example you would go to a page called Forwarding. You'll need to make up a port you want to use such as 8888. You would then enter that as the starting and ending port range. For type or Protocol select TCP. Then enter the destination address which is the static IP address of the DVR, (we'll say 192.168.100.100). Now let's say that the public IP of your router is 4.4.4.4. If I were to go to 4.4.4.4:8888 from my machine, your router would say "this traffic is to be handed off to 192.168.100.100 and would pass the traffic.
BTW, in a Sonicwall, the page is under Services so it may be named differently in a Belkin.
I hope this helps a little. Post back with specific questions and we'll try to help.
Afterthought: Depending on the software you're using, you may have to place either https:// or https:// before the public IP address. Good luck.
