http://tipline.blogspot.com/2008/05/tips-worldwidetelescope-is-live
Thanks to Alma Row for reminding me via email that the Worldwidetelescope from Microsoft is now active.
I had mentioned it back in February( http://tipline.blogspot.com/2008/02/tips-stop-what-youre-doing-and-watch.html) and now it's active. Of course, it's not yet available for the Mac, and it does require the .NET network, and it's not the easiest thing in the world to install. BUT, if you CAN meet all the requirements, it's going to be a phenomenal experience!
http://www.worldwidetelescope.org/experienceIt/ExperienceIt.aspx?Tat=takeatour - That's the tour page. You can download it here: http://www.worldwidetelescope.org/experienceIt/ExperienceIt.aspx?exp=true
It's just a shame that microsoft has this instead of someone who isn't concerned about your OS. Let's hope that a MAC version is out soon.