He lags on everything he looks at, moves, plants, paints all that sort of stuff.
Not quite, just.... without having to retype things I've said for the umpteenth time; reread what I typed in the original post.
Try disabling Vista's Aero themes, the transparency can cause issues with certain video cards.
Aero has caused no problems with blockland, turning it off does not cure this error. I have never turned off aero before while running blockland and it has worked just fine. Whatever has caused this problem was not a symptom of using aero; to my knowledge.