http://en.wikipedia.org/wiki/Internet_Explorer_8

The browser was released on March 19, 2009 for Windows XP, Windows Server 2003, Windows Vista and Windows Server 2008.[1] Both 32-bit and 64-bit builds are available. It is the successor to Internet Explorer 7, released in 2006, and is the default browser for the upcoming Windows 7 and Windows Server 2008 R2 operating systems.