<p>I'll preface this by saying I'm a C# programmer who inherited horrible code with no documentation.  I have an unmanaged C++ library wrapped with managed code that worked fine in VS2003 with .Net 1.1 Framework.  I'm trying to get it upgraded to at least .Net 2.0.</p>

<p>I have the unmanaged C++ library that was compiled with "MSVC 8.x" (thus equivalent to VS 2005, I assume).  I've been trying to migrate everything to VS2008 and still have some issues with this library at runtime.</p>

<p>My question is this: should this library work with VS2008?  Or should I be developing in VS2005 if the library was compiled with VC8.x?</p>

<p>Any thoughts would be greatly appreciated.  Thanks!</p>

It should work, I expect that you are having issues with your marshalling. It is probably stuff that was declared incorrectly for PInvoking that managed to work in .NET 1.1 but not in later versions.
You don't say what sort of problems you are having at run time, nor do you state how you access your library. For example, do you compile your library along with your project? If so, can you turn on unmanaged debugging in your C# project and step into the code you are having trouble with? How are you calling the unmanaged code? Is it through PInvoke, or do you have managed C++ wrappers?
In my experience, the best solution for calling out to a legacy unmanaged library is to add a managed wrapper library for your legacy library written in managed C++. This way you present a managed interface for your library for all .NET languages to consume and you don't have to worry about getting your PInvoke signatures correct.
Your project should look something like this.
C# Application -> Manage C++ Wrapper DLL -> Legacy DLL