the UPNP problem was the first HUGE security flaw found in xp, or atleast the first huge one released to the public. however, you can check out http://www.grc.com where Steve Gibson has some applications designed to point out and fix alot of the xp security flaws. Also there is a great deal of information as to what the exact problems are in XP, like how UPNP is a security risk.
And I believe that the traffic that problemchild is seeing is a broadcast by his pc looking for other UPNP devices on his network. the traffic should probably looks somthing like this..
your.ip.addr.here -> your.domain.here.255:1900
where you will see anything else on your network that happens to respond to broadcasts replying that the port does not exist, that is unless you have another xp system on the network that doesn't have UPNP turned off.
This traffic puzzled me as well. One LAN party I went to I was approached by the host asking me to get my norton updates and scan my pc because he thought i had a virus. Once the host saw that my box was clean with the latest updates he did a little checking. And suggested i turn off the UPNP service. I went to http://www.grc.com and got the little app "Unplug n' pray" and turned it off. The traffic stopped and they left me alone. Oddest thing in my mind that night was that I was the only person running XP.
So if you're concerned about the traffic go get that app and check your system. Upon running the program it will open a dialog that tells you that your system is either safe or unsafe and gives you the option to turn UPNP on or off depending on it's current state.
And while you're there you might want to check out some of his other applications.
