The easiest way to combat this problem is to use a router that supports dynamic DNS services and static DHCP.

-Dynamic DNS is a service (see: dyndns.com,no-ip.com) that provides you a URL (such as: mattswebcam.no-ip.com) that you can use in place of your ever changing internet (WAN) IP address. Basically when your WAN IP address changes, your router, of course knows this and updates the your DNS via "no-ip.com" automatically.

-Static DHCP- this is supported by only a few routers ( that I know of). It makes the router hand out LAN IP addresses based on the MAC address of the ethernet card. The MAC is a unique address everything ethernet device has. So if your router sees a particular MAC, it knows to give it a certain IP address. The advantage to this is that you can use port forwarding to ensure the data stream goes to, or comes from a particular computer. You can setup a DMZ, but this takes you out from behind the firewall. Also you can only setup one computer with a DMZ