Without actually looking at the specifics, port forwarding is simply a process by which network traffic directed at a particular port from the outside of your network (internet -> firewall) is sent to a specific IP address (the address of the machine you want to receive the traffic). It is rare to think that all traffic should be forwarded, nor is it wise from a security perspective but it can generally be done by forwarding a range of ports.
Assuming the post quoted is correct, the process is simple. First, log into your router (or firewall if seperate, though you'll likely need to do this step twice). Under the firewall settings all but the cheapest routers will offer you the capacity to port forward.
Traffic from ports 28910, 29900, 29901, 29920, 80, 443 (TCP) should be sent to the SAME ports on the address that corresponds to your Wii.
All UDP traffic should be forwarded, which is a range of 0 - 65535.
The latter step is almost certainly false, but it does cover all of the bases. There is simply no need to use ALL of the UDP ports on any machine that I've ever encounterd.
Your gateway and subnet can be rather easily obtained. If your Wii exists on the same network as the PC you used to post, the gateway (which is the device that marks the end of your local network, generally speaking a router or your modem, though in rare cases it may actually be your ISP) and subnet (a number that determines the valid IP range of your network, most home networks are a class C and as such correspond to 255.255.255.0).
If you don't want to go through the trouble of finding out all of this information (but you somehow have the address of your router) you can make the following assumptions that generally hold true:
Your gateway address is probably the same as your router. For most home networks, unless specifically changed, the default address is 192.168.1.1 (linksys and most lesser brands) or 192.168.2.1 (belkin), or 192.168.1.254 (2wire).
Your subnet mask is likely 255.255.255.0, and most home consumer routers don't offer the opportunity to use a wider range, though a narrower one can be set if desired. Generally speaking however, unless you specifically altered this setting it should be at the default.
I am unaware if the Wii supports DHCP or if it requires a static address. If it supports DHCP, it will be easiest if you use a static setting instead as it makes the process of port forwarding easier (there is no possiblity the address will change). If it was static, then you should know what the address is because you set it. Just keep in mind that it must be in the range specified by the subnet mask. The first three octets should match your gateway (1.1. 192.168.1.x) where x is the address you want to assign. This value should not be the same as any other value on your network.
