I find the setting to be fine under XP, but I'm not sure what to do to help the guy who is having trouble in Vista (Though they're fairly similar interface-wise).
In XP go to the control panel (Fastest way: [Command]+R, type "control" without quotes and hit enter), switch to classic view if it isn't, and double-click on "Mouse". At the top of the window, there is a tab labeled "Wheel". Click on it, and from there you can adjust your scrolling speed, or you can instruct it to scroll in a way not unlike hitting [page up]/[page down].
As far as Windows is concerned, you're using the scroll wheel in the centre of a regular three-button mouse. Normally they click as they spin, which is why the speed setting is "number of lines per click". Every time I see one of those old Apple-brand mice, I feel compelled to wear mittens.
I hope this helps... But I don't know if it works for the Vista guy.