Asp.net 4.0 & HTML 5

1) Asp.net 4.0 with Visual Studio 2010 is compatible with HTML 5. You can download the Visual Studio Service pack 1 Beta From Here

for Html 5 and CSS3 intellisense http://www.microsoft.com/en-us/download/details.aspx?id=23691

2)http://blog.reybango.com/2010/09/21/how-to-create-html5-website-and-page-templates-for-visual-studio-2010/