This is a curiousity rather than a true solution. This morning, on booting his PC, a colleague found his PC refused to browse websites and (apparently) would not connect to any network shares, yet it could FTP to an external website and ping/tracert google.com. After booting XP, and entering user details (“loading your personal settings…”) the system would idle until the network cable was pulled from the NIC. The only thing which changed is that I installed VMWare Server Console on the system the day before (not the server itself, so it shouldn’t have added virtual NICs or messed with settings).
I solved the problem by uninstalling the NIC driver and letting it re-install after a reboot, but I’d love to know what may have caused the issue!