"MSBee" is a free MS Build task that allows you to target earlier versions of the .NET Framework from within Visual Studio 2005. Out of the box, VS2005 will only allow you to compile for .NET 2.0.
This is a very helpful utility: just a few months ago I had a client balk at a project because we said "You'll either have to run side-by-side .NET 1.0 and 2.0 assemblies, or the team will have to downgrade to VS2003, or we'll have to move to command-line compiles."