Slow response on LAN/WAN caused by one machine   

Hi, I tried posting earlier, but the post didn't seem to work, so I'm hoping 
this is not a duplicate post. I apologise if the original post actually made 
it.

I have a network with 7 PCs and an IP camera, originally all running XP SP2. 
The PCs connect to a dlink gigabit switch, through a dlink gigabit router, to 
a cable modem then out to the internet.

The problem is that one of the PCs seems to kill LAN/WAN traffic. I haven't 
measured impact to LAN traffic because I don't know how. I used ping 
www.holden.com.au for the WAN. When I unplug the PC in question I get 25ms 
response time. When I plug it in, i typically get around 2000ms response. 
Sometimes it wil be fine for a period, but mostly, it kills that WAN use such 
that a 400k email too 6 minutes to download, and a website took 20 mins to 
load.

I started with the typical hardware checks;

Replaced all leads from suspect PC to switch
Tried different switch ports
Eliminated switch and ran suspect PC direct to router
Upgraded firmware on router (I originally suspected the problem was here)
Replaced the router
Flashed the BIOS on the suspect PC
Replaced NIC drivers from m/b CD on suspect PC
Downloaded NIC driver from MSUpdate & Installed
Upgraded from XP to Vista
Disabled on board NIC and installed a PCI NIC.

None of these have isolated/resolved the issue

1. What tools are available with XP/Vista that I can use to monitor & Log 
NIC traffic. I would prefer something I can install on my fie/print server, 
if available, but on the suspect PC will be fine if there are no other 
suggestions

2. Has anyone come across this before, and if so what might be the 
cause/solution? What else could I try?

3. This PC has been on the network for a almost year and there has been only 
XP Patches applied over the last 12 months. No hardware changes have occured.

4. I've tried googling a few different phrases but haven't come accross any 
useful results. Can anyone suggest some helpfu phrases or hints on how I 
might find answers if one cannot be provided here (I apologise for my lack of 
spacia thinking ability).

Any help is greatly appreciated.

thanks
Tanya

date: Sat, 17 May 2008 19:29:01 -0700   author:   Yanta