I thought I would share a few experiences changing vb.net 'code-behind' files into c# using Visual Studio 2005 for an asp.net web site.
1) Make sure you are not changing files in the wrong place - it won't work!!
2) You can leave the solution open when you do so: Go into windows explorer and rename the code file from something.aspx.vb to something.aspx.cs
3) Open the aspx html file for the file yu have changed in the solution and change the page directive to language="c#" and CodeFile="something.aspx.cs".
4) Important! save and close the aspx file before compiling. If you don't do this, the compiler will change things in the 'c#' file back to VB style - e.g. "namespace" will become "Namespace" and "try" will become "Try". It took me a while to find out.
5) Open the code file which is currently full of vb but now expecting c# and do some find and replaces to make the syntax correct. For example find and replace "If " with "if ( " and "End If" with "}" (Don't worry about indenting, you can do this later.
6) Hopefully you can work out most of the differences between C# and Vb but some of the funny ones are a) VB uses = instead of == in logical comparison. Fortunately c# will complain about this! b) If VB functions take no arguments, they are called with no brackets which in c# will cause an error which is slightly helpful as to the cause (i.e. you need ToString() instead of ToString) c) VB doesn't use brackets and semi-colons for scoping code so these will need adding.