Just as an aside - mine works fine in Vista. But, I don't use it. Reason? I have an LCD monitor, and a screen saver does nothing to save the life of the backlight. When I walk away from the machine, I simply turn off the LCD monitor by pressing a button. This guarantees that the backlight will not burn unnecessarily.
Screen savers protect CRT monitors from "burn-in." LCDs do not have that problem, so a screen saver is basically for entertainment and eye wash.
You really should chack ALL your ACPI settings. A very good one is MONITOR OFF after, say, 10 minutes of inactivity.