If you are wondering what the timelines are for Internet Explorer 8 release via Windows Update are, well, today we announced on the IE blog that users with IE 6 and IE 7 will get it pushed in the 3rd week of April 2009. The install will be opt-in.
On Windows XP and Server 2003, the update will be High-Priority. On Windows Vista and Server 2008 it will be Important
For companies who wish to manage their own deployment, they should use the free Blocker Toolkit that will block automatic delivery of IE8 via Windows Update.
If you want to Install IE 8 now, you can get it from here.