I am trying to set a wan ip alias on a 2910

I am trying to open port 80 to a lan client, but this just seems to open the router config webpage.

if I change router http management page to port 8080 this gets over the problem, is there another way?

By default the managenment port is on port 80, we normally set them to something else like 81 or 82. So in your case if you want to port forward port 80 to the LAN then you will need to change this port.