Hello,
I have not set this up myself, but I have received this info from Parag Nikhal, hope this helps.
"I consider that you have develop a site in DNN 4.0 with visual studio 2005 so in that we have a dotnetnuke's starter kit for createing a VB.NET DNN 4.0 site...
after creating a site right click on root and add a module one dialog box will open for adding a module choose language as C# in that and click OK..... then C# module will be created in same site...
major change is in web.config file....
<system.codedom>
<compilers>
<compiler language="vb" type="Microsoft.VisualBasic.VBCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089" extension=".VB" />
<compiler language="C#" type="Microsoft.CSharp.CSharpCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089" extension=".CS" />
<!-- add above line just change a PublicKeyToken as per your publickryToken-->
</compilers>
</system.codedom>
after this build a site...."