With the release of Internet Explorer 9, Windows XP is not supported anymore. There isn't a tweak or something related to bring Internet Explorer 9 in Windows XP.
According to the official requirements, Internet Explorer 9 is supported on the following platforms:
Windows Vista 32-bit with Service Pack 2 (SP2) or higher
Windows Vista 64-bit with Service Pack 2 (SP2) or higher
Windows 7 32-bit or higher
Windows 7 64-bit or higher
Windows Server 2008 32-bit with Service Pack 2 (SP2) or higher
Windows Server 2008 64-bit with Service Pack 2 (SP2) or higher
Windows Server 2008 R2 64-bit
