you guys have to understand 2 things:
there are 2 different type´s of lag, the first is
Lag caused by your connection, it causes you to freeze, or warp through the scenes. You can try this yourself by creating a server for 8 guys and letting more then 4 join. you can see your ping (which is an indication wether you have a good connection to the server or not) when you got a ping below 100 you can play perfectly fine, ideal is 30/40. if it goes up to 2000k it means the server which is using it cant provide all the clients with a proper ping.
The second type of lag is computerlag, this one is caused by the lack of good specs. By specs i mean your graphical card, memory, processor speed.
possible fixxes to solve these 2,
for lag type one, you can play around a little with these variables
cl_cmdrate
cl_updaterate
rate
i found cl_cmdrate 101 cl_updaterate 101 and rate 25000 good enough for me
type r_netgraph 3 in console and look what your choke/loss is, if it is higher then 10 tone down the values i gave you.
cl_cmdrate 40 cl_updaterate 40 rate 9999 for instance.
I´m on a 2500/358 cable connection. so if you dont have atleast some kind of equal connection dont try the values i stated first.
well as for the second type of lag, this one is caused by the hardware in your computer. the things you can do is tone the settings from high to medium or low. if that doesnt work only buying new hardware would probally fix your problem.