I have been speaking to many people in the past with Lag problems when playing on CF some of these problems are due to spyware.
If you have an issue CF has a command prompt type /ping....it will disply for you your Ping any packet losses and Fluct both packet loss and fluct should be 0.
If you see that you have Fluct run a Spyware scan....If you dont have one i recommend Spyware Search and Destroy its is free to download from here:
http://www.safer-networking.org/en/download/index.html
the creator does ask if you want to make a donation but thats up to you and not needed to use.