Ping in games

[#1]

Hi, When I try playing games online e.g. TF2 I am OK for the first few minutes and then my ping goes high and I lag. Some servers give me a warning of high ping before I get kicked.
Other than gaming my connection is fine, my download speed is around 6mb and I can download files very quickly/
Any ideas?
Thanks
Neil

[#2]

Hey,
Are you downloading at the same time as when you are gaming and see the pings increase?

[#3]

you using tg582n ?