See, these days this is just asking for trouble. Just looking at the Apache logs on my Linux firewall/etc box makes me feel unclean; I don’t wanna know what’s happening on the other ports.
I recommend you get either a hardware router/firewall, one of those 3rd party firewall programs, or at least turn on the firewall option in XP’s networking. Microsoft promises they’re fixing up their OSs 'net presence in the next service pack, but don’t hold your breath.