Serious lag

Hi
I have 2 pcs and an xbox 360 on a wired network. Up until a few months ago it worked fine. Then our pcs started to slow down and when playing online games on the 360 it can go from full ping to 1 ping making it impossible to play. My internet provider tells me the speed is fine and it appears to be ok doing a speedtest.
I just checked my connections in command prompt and have at least 10 time_waits everytime I do it.
We run vista on the pcs.

Hope someone can help
Thanks

 

time_wiats just tripled lol erm mainly got the same foreign address