1gig is ok for XP, the more the merrier, as always.
the video card could be a bottleneck, however, for that game, nothing fancy is required. I would probably say it could be the browser itself, like if you're using Firefox or Opera and you're experiencing this, I would try IE 7 or 8. Reason being, almost all websites are designed to be run/viewed with IE. Some sites simply don't work with anything but IE. As much as I am not a fan of IE, it's there for a reason. Usually I have issues with banking websites with Mozilla vs. IE.
as for ads, yes, some of them can very easily be the culprit, and if they are, it means that they potentially are trying to take over. If you can get the website address, you can easily block the site out in IE by going to security and blocking the site.