Ok, my system clock is officially dead. While my PC is on, it's fine, however, when I turn it off for long enough (let's say overnight), it drifts by the hour (my guess: capacitors (if that's the English name for "codensateur") empties itself, the when empty, clock drifts and doesn't even try to use the battery).
No, it's not the CMOS battery. I replaced it a month ago.

So, what I'm looking for now is a way, when XP starts, to sync my clock to a public (S)NTP server. The one provided with XP syncs every week, which is usually 6 days too long. So, I'd like a program that when XP starts up, syncs, then leaves the pc alone, or syncs and then idles for a period of time that I choose.
Why am I asking here? Because google will return a lot of programs, none of which I trust about not spywaring me, so I want something that is tested and known to be good and not installing crap on top of it.