Does your website use Microsoft ActiveX® controls?
Does your website allow users to download files?
Does your site use pop-up windows?
Does your website depend on the Microsoft Java Virtual Machine (MSJVM)?
Does your website use HTML dialogs?
If you have answered yes to any of the questions above be sure to check up
How to make your web site work with Microsoft® Windows® XP with Service Pack 2 (SP2)
as things might stop working as you'll install XP SP2.