As BC said, IE8 is the newest version for XP. That said, you really shouldn't run an out of date browser so I would strongly recommend that you look into something like Chrome or Firefox as running an out of date browser opens you up to loads of security vulnerabilities.
Also, if you do still insist on using XP - Update to Service Pack 3. There is no reason to stay on SP2 and by doing so you are leaving yourself open to even more vulnerabilities than by still running XP.