Placing a TAP-Windows device in TAP mode

I am using TAP-Windows (from the OpenVPN project) to create an interface as described here and here. I am basing my code of the example provided in the first article:

const string UsermodeDeviceSpace = "\\\\.\\Global\\";
string devGuid = GetDeviceGuid();
IntPtr ptr= CreateFile(UsermodeDeviceSpace+devGuid+".tap",
    FileAccess.ReadWrite,
    FileShare.ReadWrite,
    0,
    FileMode.Open,
    FILE_ATTRIBUTE_SYSTEM | FILE_FLAG_OVERLAPPED, 
    IntPtr.Zero);
int len;
IntPtr pstatus = Marshal.AllocHGlobal(4);
Marshal.WriteInt32(pstatus, 1);
// Set media status to connected
DeviceIoControl (ptr, 
    TAP_CONTROL_CODE (6, METHOD_BUFFERED), pstatus, 4,
    pstatus, 
    4, 
    out len, 
    IntPtr.Zero);
IntPtr ptun = Marshal.AllocHGlobal(12);
Marshal.WriteInt32(ptun, 0, 0x0100030a); // 10.0.0.1, Interface address
Marshal.WriteInt32(ptun, 4, 0x0000030a); // 10.0.0.0, Network
Marshal.WriteInt32(ptun, 8, unchecked((int)0x00ffffff)); // 255.255.255.0, Netmask
// Config TUN
DeviceIoControl (ptr, 
    TAP_CONTROL_CODE (10, METHOD_BUFFERED)
    ptun, 
    12,
ptun, 
    12, 
    out len, 
    IntPtr.Zero);
tap = new FileStream(ptr, FileAccess.ReadWrite, true, 10000, true);
// Setup callbacks, etc. here.
while (true)
{
    // Read from the device
}

It seems that the device is in TUN mode - while I get the payload of the packets, the ethernet headers are not included. What is the correct way to force the interface to operate in TAP mode?

I am running the code on a 32 bit Windows 7 virtual machine in VirtualBox.

I'm working with this example just now. I realize that when you make this call:

IntPtr ptun = Marshal.AllocHGlobal(12);
Marshal.WriteInt32(ptun, 0, 0x0100030a); // 10.0.0.1, Interface address
Marshal.WriteInt32(ptun, 4, 0x0000030a); // 10.0.0.0, Network
Marshal.WriteInt32(ptun, 8, unchecked((int)0x00ffffff)); // 255.255.255.0, Netmask
// Config TUN
DeviceIoControl (ptr, 
    TAP_CONTROL_CODE (10, METHOD_BUFFERED)
    ptun, 
    12,
    ptun, 
    12, 
    out len, 
    IntPtr.Zero);

it's when the interface is placed in TUN mode. What I did was just to ignore this (I did't make this call to DeviceIoControl), and then all packets where received by the File Stream.