Port Forwarding involves forwarding the Public (usually) Dynamic IP, whatever it is, to a fixed LAN IP (your XP box).
So, You CAN (and should) assign your XP box a static LAN IP (usually 192.168.something) so that the port forward config does not become stale when your XP box gets a new IP if it is configured for DHCP or "Automatic Configuration." This has nothing to do with the dynamic IP assigned by your ISP, but your should start here, or you'll end up chasing IPs in more than one place -- Port forwarding is a static config, so if your XP box gets a different IP from the one that you confgured in the router's port forward config, the forwarding won't work anyway until you re-config the router.
You have a router I never heard of, so you need to either find the router docs online, or get another router. Otherwise, without the router docs, you'll have to "feel" your way around the router config -- port forwarding is all the same -- you forward a TCP port or range of ports [you only care about the DNAS PortBase] to a LAN IP [the IP of your XP box] -- Nothing more or less.
Now, part 2...
Your ISP certainly gives dynamic IPs, but port forwarding has nothing to do with that (that is to say, it does not care what the public IP is) -- it only forwards the public IP whatever it currently is to the PC's LAN IP.
So what can you do?
A lot of people here use a free DNS service like No-IP.com
to get a DNS name like mywebradio.no-ip.com
that can be used wherever a dotted-numeric IP address [nn.nn.nn.nn] is called for -- to make this happen, you also need to run an update client on your XP box that will make sure that the DNS name you created stays updated to your current IP address. You have to create an account and download the update client [DUC], but then you're done.