First lets get a few things straightened out. Delphi.NET is both a language and a set of runtime libraries which attempted to recreate the RTL/VCL on the .NET platform.
Borland Development Studio is an IDE designed to edit multiple languages: Delphi, C++, C#, Delphi.NET.
If your intention is to port a Delphi.NET application to C# there are a few tools you can use. RedGate's .NET Reflector can generate C# from any .NET assembly regardless of the language that was used to write the assembly. I found it to be fairly useful at converting a Delphi.NET application to C#. Note: The generated code will still have dependencies on the RTL/VCL so you will still have to replace these with standard .NET equivalents.
If you are doing a Borland C# to VS C# port at least you're already in the same language. You'll just have to deal with library dependencies for the most part. If you already have the code working in BDS 2006 you can save yourself some trouble by replacing any borland-specific dependencies with standard .NET ones before you move to Visual Studio.
With proper separation of concerns and wrappers around third party libaries this is fairly straightforward. Unfortunately this is rarely the case. If your project is like most RAD style projects the business logic is embedded directly into the UI and library dependencies are directly woven into your code (this is rampant on any platform so don't think I'm singling out fans of Borland/Inprise/Codegear/Embarcadero). If this is the case you have your work cut out for you.