there is alot of thing to get less lag, here are some
1. get a friend too host a game, I have a 512k cable, i host a game for a friend of mine and he gets a good ping and does not lag
2. chosse the right map, some maps, with alot of water for example will lag more then one without.
3. Dont run anything in the background, anything like a internet page, anything like that you will need to close
4. Music! dont have it on!
I cannot think of anything else right now, you can aways hosta dedicated server, if you have 2 comps, or u cannot join yourself.