I can't tell you exactly because I don't use Windows XP, but this happened to a member of my forums - she kept getting cached versions of pages on my forums - eg. she would make a post but it won't show up.
We found out that Windows XP kept changing her "Check for new pages" in Internet Options to "Never". In the end, she traced it back to the new feature of XP to make a backup of your Windows setting, and restore the backup every couple of hours. Which is annoying if you have made any setting changes.