Yes, you can develop different web forms (pages) in two different languages. Same page can't have two different languages.
The page directive for c# will be
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default2.aspx.cs" Inherits="Default2" %>
and VB.Net will be
<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="_Default" %>
I have tried this in 2008 express editions, not in 2010