I lag, but I've noticed that its always when I start mid game, or others (WHICH HAPPENS WAY TOO MUCH) join mid game.
Also, check to see if other programs are running, I don't know Vista, so I couldn't tell you how. I know if you check out other game sites (Quake 4 MMO for example) have info for speeding up lag time. (Once again, with Vista I'm fuckin' clueless).
For WinXP the Quake 4 site called for check disk and defrag, along with checking to see if other process's are running. I don't know if Vista has multiple login users, like windows. Sometimes they just switch users and not log off, and they leave programs open and running.