I have a program that I need to create a DLL for, hopefully in C#. The program is written in Delphi and I have an interface file to code to. The interface uses the stdcall
Out of curiosity, why are you hoping to write a .dll that's intended to be used from a native application in C#?
Managed C++, Delphi for .Net and now Delphi Prism all support this out of the box using unmanaged exports. By design, C# and VB.net don't. Not sure why. But as Cobus mentioned, you can kind of hack around this. Do so at your own risk.
In addition to Hydra from RemObjects, AToZed is introducing CrossTalk.