C# Definition:

    /// <summary>
    /// Contains information about the state of the mouse.
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct RawMouse
    {
        /// <summary>
        /// The mouse state.
        /// </summary>
        public RawMouseFlags Flags;
    /// Value type for raw input from a mouse.
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct RAWINPUTMOUSE
    {
        /// <summary>Flags for the event.</summary>
        public RawMouseFlags Flags;
        /// <summary>If the mouse wheel is moved, this will contain the delta amount.</summary>
        public ushort ButtonData;
        /// <summary>Flags for the event.</summary>
        public RawMouseButtons ButtonFlags;
        /// <summary>Raw button data.</summary>
        public uint RawButtons;
        /// <summary>Relative direction of motion, depending on flags.</summary>
        public int LastX;
        /// <summary>Relative direction of motion, depending on flags.</summary>
        public int LastY;
        /// <summary>Extra information.</summary>
        public uint ExtraInformation;
    }

VB Definition:

Structure RAWINPUTMOUSE
Public TODO
End Structure

User-Defined Field Types:

None.

        [StructLayout(LayoutKind.Explicit)]
        public struct Data
        {
        [FieldOffset(0)]
        public uint Buttons;
        /// <summary>
        /// If the mouse wheel is moved, this will contain the delta amount.
        /// </summary>
        [FieldOffset(2)]
        public ushort ButtonData;
        /// <summary>
        /// Flags for the event.
        /// </summary>
        [FieldOffset(0)]
        public RawMouseButtons ButtonFlags;
        }

Notes:

None.

        public Data Data;

        /// <summary>
        /// Raw button data.
        /// </summary>
        public uint RawButtons;
        /// <summary>
        /// The motion in the X direction. This is signed relative motion or
        /// absolute motion, depending on the value of usFlags.
        /// </summary>
        public int LastX;
        /// <summary>
        /// The motion in the Y direction. This is signed relative motion or absolute motion,
        /// depending on the value of usFlags.
        /// </summary>
        public int LastY;
        /// <summary>
        /// The device-specific additional information for the event.
        /// </summary>
        public uint ExtraInformation;
    }

    /// <summary>
    /// Contains information about the state of the mouse.
    /// </summary>
    [StructLayout(LayoutKind.Explicit)]
    public struct RawMouse
    {
        /// <summary>
        /// The mouse state.
        /// </summary>
        [FieldOffset(0)]
        public RawMouseFlags Flags;
        /// <summary>
        /// Flags for the event.
        /// </summary>
        [FieldOffset(4)]
        public RawMouseButtons ButtonFlags;
        /// <summary>
        /// If the mouse wheel is moved, this will contain the delta amount.
        /// </summary>
        [FieldOffset(6)]
        public ushort ButtonData;
        /// <summary>
        /// Raw button data.
        /// </summary>
        [FieldOffset(8)]
        public uint RawButtons;
        /// <summary>
        /// The motion in the X direction. This is signed relative motion or
        /// absolute motion, depending on the value of usFlags.
        /// </summary>
        [FieldOffset(12)]
        public int LastX;
        /// <summary>
        /// The motion in the Y direction. This is signed relative motion or absolute motion,
        /// depending on the value of usFlags.
        /// </summary>
        [FieldOffset(16)]
        public int LastY;
        /// <summary>
        /// The device-specific additional information for the event.
        /// </summary>
        [FieldOffset(20)]
        public uint ExtraInformation;
    }