Internet Explorer 8 Beta 2 is available for download. You can download it from: http://www.microsoft.com/windows/internet-explorer/beta/
 
IE team has detailed information on their blog (IEBlog):
Internet Explorer 8 Beta 2 Now Available
Upgrading to Internet Explorer 8 Beta 2
Introducing Compatibility View
IE 8 Performance
Part I: Better Everyday Browsing 
 
Links: http://delicious.com/vikasahuja/IE8