I have noticed this problem on a 4 machines, around the time when my watchguard firebox would not be able to reach the internet, and it would say lost connection. Theyb are all XP machines. Its like something is making them transmit a bunch of packets, and its overloading the firebox and inturn making my internet connection drop for like 2 minutes every couple of hours.
When i do a status on 4 xp machines in the building they are saying transfered 56,342,423,234 recieved 312,132 - which is f'd up. I have a virus protection on both machines, updated it found nothing, and no spyware installed.