Update your Internet Explorer (which is what ZKL uses... yes, I know) as a first step.
You need to determine if your lag is CPU or connection based. If your housemates are torrenting, then yeah, you generally can't play games when torrenting (Zero-K deals with it better than most). It shouldn't grind to a halt unless it is disconnecting you (In which case, it will tell you). Look at the player list, you have icons there that go from green to red as your CPU or ping load gets too high.
