It sounds like it's the Daylight Savings Time bug.
This year, various places (including most or all of the USA) changed the date when Daylight Savings Time went into effect. Microsoft Windows requires an update, or it will follow the old schedule and get mixed up, etc. It's especially nice since many networked computers rely on a time server, and will thus systematically re-set to the wrong time; and some M$ network software reportedly requires clocks to be in sync in order to authenticate
. Win 2003 and Win XP SP2 should patch it if you go to the Microsoft Update web page and run their software (especially if you have their insulting "Genuine Advantage Genuinization Tool" or whatever-the-frack they call it). Earlier Windohs sufferers (including Win2K, and XP SP1 it appears) need to manually install a patch, which does exist but isn't the easiest thing to find...
As for why the frick Microsoft Windohs won't even let you set your own system clock manually and have it not be a problem, well, I'd chalk that up to typical M$ over-engineered "we know what you want - here, let us jam it down your throats" design.
PvK