Updating windows 98 to xp
It's likely (as Derek says) that if your machine is running Win98, you just don't have enough horsepower (for lack of a better term) to run XP decently. See here: need to run in "Windows 2000 SP4" compatibility mode, BUT maybe not. Even with 6.1 I had problems with online banking, paypal and ebay.
I'm not sure if alternate browsers have the same problem.
HOW TO: Troubleshoot Windows XP Setup Problems When You Upgrade from Windows 98 or Windows Me Microsoft Knowledge Base Article: 310064 - This article describes troubleshooting steps that you can use if you have problems when you try to upgrade to Windows XP from Microsoft Windows 98, from Microsoft Windows 98 Second Edition, or from Microsoft Windows Millennium Edition (Me).
And be sure to back up your data before you start your upgrade.It is fast, lightweight and not anything near as old as your IE.