int __stdcall procname(HWND mWnd, HWND aWnd, char *data, char *parms, BOOL show, BOOL nopause)

For instance, no idea how I'd come up with the HWND in VB.NET :P

HWND is MyControl.Handle, e.g. Form1.Handle, PictureBox1.Handle, its a 32-bit unsigned integer and msdn recommends using the type 'System.IntPtr' for storing it in .NET applications

If you look up the types on msdn you can work out how to convert most C/C++ types/structs into .NET