Here’s where you can download IE8 Beta 1, together with direct download link to get the setup installation executable file from Microsoft Download Center server.

Internet Explorer 8 Beta 1 for Windows Vista and Windows Server 2008 (x86)
http://go.microsoft.com/fwlink/?LinkId=110325
Direct Download: IE8-WindowsVista-x86-ENU.exe

Internet Explorer 8 Beta 1 for Windows Vista x64 Edition and Windows Server 2008 x64 Edition
http://go.microsoft.com/fwlink/?LinkId=110328
Direct Download: IE8-WindowsVista-x64-ENU.exe

Internet Explorer 8 Beta 1 for Window XP SP2
http://go.microsoft.com/fwlink/?LinkId=110324
Direct Download: IE8-WindowsXP-x86-ENU.exe

Internet Explorer 8 Beta 1 for Windows Server 2003 SP2 (x86)
http://go.microsoft.com/fwlink/?LinkId=110326
Direct Download: IE8-WindowsServer2003-x86-ENU.exe

Internet Explorer 8 Beta 1 for Windows Server 2003 SP2 x64 Edition and Windows XP SP2 Pro x64 Edition
http://go.microsoft.com/fwlink/?LinkId=110327
Direct Download: IE8-WindowsServer2003-x64-ENU.exe

IE 8 features improvements in Cascading Style Sheets (CSS) and layout, programming model, performance, reliability, usability and service integration. Other features include contextual services to quickly access a service from any webpage named Activities, WebSlices for content subscribing within webpage, Favorites Bar has replaced Links bar, Automatic Crash Recovery and improved Phishing Filter. Details can be read here.

The release note for Internet Explorer 8 Beta 1 can be read here. Note that IE8 is still in beta stage, and the release is probably mainly meant for developers, webmasters, bloggers, website designers and publishers to test the compliance of their sites with IE8. Average users will likely see weird rendering of web pages in IE8.