Yes you can do this in Visual Studio and it is called Multi-Targeting.
Scott Guthrie has a great blog-entry on Multi-Targeting Support in Visual Studio.
VS 2008 was the first release of
Visual Studio that included
multi-targeting support for .NET.
What this meant was that you could use
VS 2008 to create and edit not only
.NET 3.5 projects, but also .NET 3.0
and .NET 2.0 projects as well. This
allowed developers to more quickly
upgrade and take advantage of new
Visual Studio tooling features –
without having to necessarily require
the newer version of .NET to be
installed on the clients and
production servers running their
applications.
Cheers