We have vista cctv cameras and a DVR box and cannot see the pictures remotely

1 the dvr box does not have dhcp so we cannot see it on the router. we can give it a fixed ip address.
we have nicked an ip address from a non functioning webcam and can see pics inside the local network but not outside
we can log on to the DVR box but no pics
I am going to site to check the port forwarding which BT say is ok as a check.
and check with sofware suppliers about port needs. It seems like a firewall problem to me but why cant the router see the fixed ip device
how do you tell it to give a fixed ip address to a device which it can see and ping anyway.?
life is interesting today
yours david