Date and Time problem

Hi,

I've been running the same XP SP2 setup for a long time and a couple
of days ago I noticed the time and date had got set to incorrect
values. I reset them but next time I logged in the problem was back -
the date was set to sometime in 2006.

My first thought was the RTC battery had died but I checked the time
in the BIOS then switched off and unplugged the machine for a day.
The result was the BIOS showed the correct time so I don't believe it
is the CMOS / RTC battery that is at fault.

The problem seems to occur whenever I run Windows and it has me
stymied. I noticed that the time/date properties dialog on this PC
has an "inthernet time" tab that is missing from my work PC, I tried
unsetting the time server from the internet flag but this did not fix
the problem.

Any ideas would be most gratefully received.

Thanks,

Mike