hi samwise,
Normally for setting remote viewing which u can access over internet the concept is..
1-the dvr have to identify the modem by ip (gateway)
2-the modem have to identify the dvr by ip (dvr's ip)
3-register hostname which support the dvr and modem.(dyndns.com/dlinkddns.com lots of domain u may search )
so hope my little info helps,