As of this date (10/22/09) my recommendation is not to install IE8 on XP. I had it installed for over two months after having used v. 7 for about 4 months. IE8 was slow to load, slow to launch tabs, and just slow overall … like a fat hog. Don’t do it to yourself … wait until MS makes a decent update. I reverted back to 6, but missed the tabs, so now I am once again happy with the performance and features in 7.
Good Luck! =)