Depends where your code is. If it is all in separate code-behinds you should be ok. You can't mix vb and c# in the same code-behind or in the app_code folder though.
Not sure what the issue is, but it definitely is possible. Using the codesubdirectories tag in the web.config even lets you add subdirectories to App_Code and you can have vb in one and c-sharp in the other.
are you talking about .net 1.0 ?
if yes, then that's grate. :)
do you know any link for more information ?
I know you can if you are using Visual Studio to develop the project. Visual Studio will allow VB.Net and C# to be blended. I think Visual Web Developer will too but I am not really sure.