Well, speaking of now, its best option to upgrade to VS2008.

Till VS2008 (SP1) released, there were Visual Studio 2005 extensions for .NET Framework 3.0, which enabled developers work with .Net 3.0 right away without waiting for VS2008.but now these are not  supported by Microsoft for VS2005 as well not available for download officially from Microsoft since June 2008 I suppose.

(Plus you need compilers for 3.5 features like LINQ etc...VS2005 anyway wouldnt have these)