Go and have a look at VST.NET. http://vstnet.codeplex.com
VST.NET provides a managed framework that will make writing plugins very easy. VST.NET also supports writing a host for (unmanaged) plugins. Get the latest version from source control to have all the bug fixes. If you have any questions, just leave them on the discussion board on codeplex and I will try to answer them as quickly as possible. Hope it helps.
