If you're using Windows XP, I think IE8 is the latest compatible version of IE. But it's more secure to switch to Safari, Firefox or Chrome, even though the latest versions of these browsers too may possibly not be compatible with XP.
You may still need to use IE8 occasionally for certain Microsoft websites (they annoyingly insist on this, or the services these sites offer won't work). But you should really upgrade to Windows 7, or Linux, or buy a Mac.