You don't specify what platform you're running the server on.
If Linux, this is simple as pie. Run the following (as root), and put it into your startup scripts somewhere:
/sbin/iptables -t nat -A PREROUTING -p tcp -m tcp --dport 80 -j REDIRECT --to-ports 7080
This basically mirrors port 7080 to port 80. Connecting to one is exactly the same as connecting to the other.