Hi JimR,
I had a setup like that at my old house. I have yet to set it up for my new house. I would echo the comments about security above because my logs used to show hundreds of break in attempts a day from all over the world.
I used a small business broadband account with fixed IP addresses, but they are getting more difficult to get as the pool of IPv4 addresses is exhausted and a lot of the off the shelf kit will not work with Ipv6 yet.
It is important to set up a DMZ to isolate your home network from the 'outside' bits of the system. So your existing router becomes the outside router and the dvr plugs into that and you need a second router (without adsl modem) as the inside firewall and all your home pcs attach to that.
The system worked really well and I was able to monitor 4 cameras in real time from my phone/ laptop/ office PC.
You can build your own system from an old PC and I would recommend the free zoneminder software which runs on linux.
HTH
EG