Windows xp network problems

Hello guys , i have a big big problem.

At the company that i work for there are like 4 pcs that are sending and recieving a lot of packets to the point that the network is down.

we think that it might be a virus, we run all the antivirus that you could posible think of and nothing so far.

we have replace all the hardware, hub , nic and nothing the network after 5 minutes it goes down.

if anyone of you could give me a hand i will apriciate it.

Thanks a lot

Check what services are running on the computers.

We had someone here at work do something funny to his PC and it though it was a print server and this PC was giving out like 2 GB's a data at least a day.

How did you determine these 4 PCs were the culprits? You had to scan the network for traffic to do so. What kind of traffic were these machines spewing?

Plus I'm assuming you took them all offline and are troubleshooting them and reintroducing them to the network one at a time with careful monitoring, right?