I second the battery issue. Here are some other things to check. As you know computer clocks are "quartz" they aren't exactly precise, and may be fast or slow occasionally. Windows XP has an internet time client built in, what happens is it sync's up with the Atomic Clock once a week or so.
Double click on your clock in the lower right hand corner - Click on the Time Zone tab, verify it is set the right time zone. Try checking/unchecking the automatically adjust for Daylight Saving Time, I had time issues during the last DST change, since congress changed it, go figure... It would have been solved with automatic windows updates (which I suggest to be left on for novice, intermediate users). Anywho... Click on the Internet Time Tab, Make sure the automatically synchronize with an internet time server is checked. Select a time server from the drop down then click Update now...
If this doesn't fix it, try unchecking the checkbox on the internet time tab. Go to the Date & Time tab then manually adjust your time from there. See if this helps.
It is easy to blame the motherboard, however there are certain things and only time will tell, (pun intended) what the correct diagnosis and solution is.
Cheers and reply if you have any questions, or anymore.