I am wondering if every single field of a struct needs to be completely
attributed or if the runtime will marshall standard types "automagically"...

This would be the PInvok'd api call:
[DllImport("mywork.dll", CallingConvention = CallingConvention.StdCall,
CharSet = CharSet.Ansi)]
public static extern int GetSomeData(ref MYSTRUCT myStruct);

For example, given this struct:

[StructLayout(LayoutKind.Sequential,Pack=8)]
public struct MYSTRUCT
{
   [MarshalAs(UnmanagedType.I4)]
   public int    iFieldOne;

   [MarshalAs(UnmanagedType.U4)]
   public uint dwFieldTwo;

   [MarshalAs(UnmanagedType.U2)]
   public short  wFieldThree;

   [MarshalAs(UnmanagedType.Bool)]
   public bool bFieldFour;

}

would this be functionally the same as:

[StructLayout(LayoutKind.Sequential,Pack=8)]
public struct MYSTRUCT
{
   public int       iFieldOne;
   public uint     dwFieldTwo;
   public short   wFieldThree;
   public bool    bFieldFour;
}

Thanks in advance,
Brian Manlove