Short answer, No!
Longer answer... is still no, but lets go through the reasons it is so;
Similar to, that you can't use C# v2.0 features without at least VS 2005 and you can't use C# v3.0 features without VS 2008; it is that you cannot use EF v4.0 in VS2008.
Still a 'why'? Follow on...
Because EF v4.0 requires .NET v4.0(that is, 4.0.30319.1 to be exact - stable release out in the market, approximately 38 days ago); which means EF v4.0 is actually a part of .NET v4.0 - And, 3.5 uses CLR v2.0 while 4.0 uses CLR v4.0.
Among its many new improvements, Visual Studio 2010 introduces the much-awaited Entity Framework 4.0 and WCF Data Services 4.0 (formerly ADO.NET Data Services), which together simplify how you model, consume and produce data.
So to conclude: This means,
- .NET v1.0 was used with VS2002 having C# v1.0
- .NET v1.1 - VS2003
- .NET v2.0 - VS2005 - C# v2.0
- .NET v3.0 - Useable in VS2005
- .NET v3.5 - Visual Studio 2008 having C# v3.0
- .NET v4.0 - Visual Studio 2010 with C# v4.0
And according to Jon Skeet on SO, C# v5.0 contains major new speculated features such as Meta Programming.
If this makes you interested more in v4.0, checkout what's new in the latest .NET Framework.
1. C# Indepth by Jon Skeet: http://csharpindepth.com/Articles/Chapter1/Versions.aspx
2. .NET Frameworks: http://en.wikipedia.org/wiki/.NET_Framework
3. Microsoft .NET Framework: http://msdn.microsoft.com/en-us/netframework/default.aspx
4. .NET Framework Evolution Map: http://bloggingabout.net/blogs/fernando/archive/2009/01/11/net-framework-release-map.aspx