Many Windows applications requires .Net 3.5 yet it is not pre-installed on Windows 8 Preview.
Microsoft has published an article to help user enabling .Net 3.5 support in Windows 8
The .NET Compact Framework version 3.5 expands support for distributed mobile applications by including the Windows Communication Foundation (WCF) technology. It also adds new language features such as LINQ, new APIs based on community feedback, and improves debugging with updated diagnostic tools and features.
KUPA 