Beh... non l'ho provavo [ancora...], ma Simone
dovrebbe essere contento... 
This
is a cool idea - use the VS2005 IDE for your VS2003 projects. Tested, worked
for me. I wonder if the changes in web projects for 2005 will allow setting up
an ASP.NET 2003 template...
If the LINQ
Preview can use the C# 3.0 compiler with VS 2005 there's nothing wrong with
using the C# 1.1 compiler with VS 2005. (If you really have to 😛) The VS
2005 project templates is really simple to extend and I've compiled a small
installer to add two new project templates to your available C# templates that
makes use of the C# 1.1 compiler. One for Class Libraries and a Console
Application template.
The MSI can be downloaded here.
To add more templates follow the standard
procedure for creating a custom template and add the following line to the
resulting .CSP file to import the C# 1.1 settings (Everett targets is a file
compiled from Jomo Fisher's
ready-made 1.1 msbuild file and should be installed if you run the
installer):
<Import
Project="$(ProgramFiles)\Everett\Everett.targets" />
With this
template you can use the IDE features but still compile for the older framework.
There's plenty
information on MSDN on creating your own project templates. Especially
useful if you setup the same projects often. ie. Unit Tests with a different
testing platform etc.
<disclaimer>It worked on my machine with
Beta 2 installed but I haven't tested it anywhere else...I assume the RTM
templates works exactly the same way.</disclaimer>
Source: Impersonation
Failure : C# 1.1 Project Templates for VS 2005
Fonte: [link] C# 1.1 Project Templates for VS 2005