A dynamic IP does not change every few minutes. My ISP delivers IPs via DHCP which is 'dynamic' and I've had the same IP address for over two years. Unless you have dial-up which would be a bad idea for running a game server, DynDNS is fine. If you are going to host a game server, and have no other computers acting as a server, I advise to set the computer you will host on as a DMZ if your router supports it; if you do this though, it is advisable to have a firewall on the server machine and keep the machine updated. If you are going to port foward, just foward the port the application listens on, or a small range of ports.