how are you connecting? wired? wireless? powerline?
If running on cat5 wired connection to your router, possible latency can occur if the cable is damaged, you could also swap the filter on the phone line, if these become faulty they introduce a lot of lag. (Both of these are very cheap to replace)
If using wireless for gaming the short answer is dont as it can drop connection and be laggy as well.
If using powerline adaptors make sure they are on the same ringmain for best performance, they will still connect of different spurs in your supply but it adds a little lag and dont run them via extension cables, extension cables will add latency to your connection.
Make sure you have run a full AV / Spyware scan and that you are not being used as some kinda spam relay (AVG and Spybot are good). Ensure you are not running any kinda torrent software or download manager on startup, type msconfig into the seach bar of windows and disable all useless stuff from the startup tab.
And you could also try the following sites to get a good idea of your connection speeds - http://www.pingtest.net/ and http://www.speedtest.net/
good luck and try some battlefield bad company 2, silkroad online indeed