try connecting to a closer server location .. get a faster isp ... limit the amount of programs ur using for online ppurposes while chatting ..... those are the only ways i can think of that would do what ur asking?
If your lag issue is with others you are chatting with, try getting on the same server as they are. Will not decrease network lag, but at least you will all be 'together'.
Open DOS and ping all the servers on your network and choose the fastest one based on the times you receive. Get your friends to do the same. Then over-all you will have the best connections.