http://www.pixelstudio.nl/?p=204

/*
* Custom fullscreen and Borderless window script by Martijn Dekker (Pixelstudio)
* For questions pls contact met at martijn.pixelstudio@gmail.com
* version 0.1
*
*/

using System;
using System.Collections;
using System.Runtime.InteropServices;
using System.Diagnostics;
using UnityEngine;

public class WindowMod : MonoBehaviour
{
public Rect screenPosition;

[DllImport("user32.dll")]
static extern IntPtr SetWindowLong (IntPtr hwnd,int  _nIndex ,int  dwNewLong);
[DllImport("user32.dll")]
static extern bool SetWindowPos (IntPtr hWnd, int hWndInsertAfter, int X, int Y, int cx, int cy, uint uFlags);
[DllImport("user32.dll")]
static extern IntPtr GetForegroundWindow ();

// not used rigth now
//const uint SWP_NOMOVE = 0x2;
//const uint SWP_NOSIZE = 1;
//const uint SWP_NOZORDER = 0x4;
//const uint SWP_HIDEWINDOW = 0x0080;

const uint SWP_SHOWWINDOW = 0x0040;
const int GWL_STYLE = -16;
const int WS_BORDER = 1;

void Start ()
{
SetWindowLong(GetForegroundWindow (), GWL_STYLE, WS_BORDER);
bool result = SetWindowPos (GetForegroundWindow (), 0,(int)screenPosition.x,(int)screenPosition.y, (int)screenPosition.width,(int) screenPosition.height, SWP_SHOWWINDOW);
}

}