The port forwarding configuation page on internet routers, forwards user defined ports to user defined IP address on the LAN side of the router.
Is it a huge problem to assign a static IP address? If so, you might consider gotomypc.com. If your LAN isn't that big, you should consider moving to static addressing for it anyways. A lot of problems and event log errors will be avoided if you don't run DHCP.
I know PC Anywhere can scan a local subnet for hosts to connect to, but I don't believe you can connect over the internet to a router, and then this feature will "kick in" and give you a list of hosts.
Good luck.
Matt J.
Please always take the time to backup any and all data before performing any actions suggested for ANY problem, regardless of how minor a change it might seem. Also test the backup to make sure it is intact.