I had the same problem on my computer, was ages ago, and I am pretty sure it had something to do with a windows update and the network card I had. At some point I could use the internet, and browse the network, but transfering files was rediculously slow. But when I changed something, I couldn't go in the internet anymore, but browsing the network was fine, and transfers on the network went back up to normal speeds.
I reinstalled windows xp 5 times during the month it was happening, and then replaced the network card. Things all work fine now, so I am not sure if it was a windows update, or a dodgy network card error (I am pretty sure it was a windows issue).
It could be that something in the TCP/IP of XP was corrupted, and there is some way of actually reinstalling TCP/IP, but its not a simple, click here, click there, and whala, its uninstalled and since my problem is no more, I paid little attention to the article... but I will have a dig around, and see if I can come up with the magazine it was in.
Has Sony been able to fix the issue?
Daniel