Redirecting with pf.conf

[Budster]

I am currently running an OpenBSD router with NAT and DHCP and whatnot. Right now, I have pf.conf configured for simple things. What I want to do is redirect a port on an internal server (port 5800) for vnc so I can access the vnc from outer locations. What I'm looking for is to route server1:5800 to router(externalip):80 for webserver based access. From there, I can use a simple dyndns and connect right to it. All I need is help with the command and whats possible. Thx