Have you been to the XP update site? There's usually some fixes for internet explorer and maybe an update if you've just put XP on. Maybe that will change it?
I'd recheck your internet connection settings and possibly try the connection setup wizard incase something didn't transfer correctly from the old settings.
You could also go to click here and doanload firefox, if the problem occurs with that aswell I'd think it was a system setting, if it doesn't then it's more likely to be in internet explorer setting.