[General Questions and Answers] gciochina:
Okay. With the delivery set for tonite, I've managed to pull it through. In order to do this, we have to get the handle of the task Bar, using p/Invoke FindWindow("HHTaskBar",...). Then using a Graphics object created from the device context of the window "found" above, we paint a picture over the "OK" button (the form must have it's properties set to MinimizeBox = false and ControlBox = true, in order for the custom WndProc to handle messages when clicking the region of the task bar where we are painting. Below is the code sample. Cheers mates :)

public class MyForm : System.Windows.Forms.Form
{
#region members and delegates
delegate IntPtr WndProcDelegate(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam);

[DllImport("CoreDll.dll", SetLastError = true)]
public static extern IntPtr FindWindow(string className, string WindowsName);

[DllImport("coredll.dll", EntryPoint = "GetWindowLong")]
private static extern IntPtr GetWindowLong(IntPtr hWnd, int nIndex);

[DllImport("coredll.dll")]
static extern int SetWindowLong(IntPtr hWnd, int nIndex, IntPtr newWndProc);

[DllImport("coredll.dll")]
static extern IntPtr CallWindowProc(IntPtr lpPrevWndFunc, IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);

[DllImport("coredll.dll")]
public static extern IntPtr GetWindowDC(IntPtr hWnd);

[DllImport("coredll.dll")]
public static extern int ReleaseDC(IntPtr hWnd, IntPtr hDC);

private const int GWL_WNDPROC = -4;
private static WndProcDelegate newWndProc;
private static IntPtr oldWndProc = IntPtr.Zero;
bool userPressed = false;
ResourceManager resManager;
#endregion

#region ctor
public MyForm ()
{
InitializeComponent();
}
#endregion

#region meths
private void InitializeComponent()
{
this.ControlBox = false;
this.Closing += new System.ComponentModel.CancelEventHandler(this.OnClosing);
this.Load += new System.EventHandler(this.OnLoad);
resManager = new ResourceManager("PATH_TO_PICTURE", Assembly.GetCallingAssembly());
}

private void OnLoad(object sender, EventArgs e)
{
newWndProc = new WndProcDelegate(WndProc);
oldWndProc = GetWindowLong(this.Handle, GWL_WNDPROC);
int success = SetWindowLong(this.Handle, GWL_WNDPROC, Marshal.GetFunctionPointerForDelegate(newWndProc));
}

public IntPtr WndProc(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam)
{
//we are targeting a specific sequence (31 , 273) that will tell us when the user clicks on the picture
IntPtr retVal = IntPtr.Zero;

switch (msg)
{
case 273:
if (userPressed)
{
userPressed = false;
Execute();
}
break;
case 31:
userPressed = true;
break;

default:
if (msg != 307)
userPressed = false;
DrawCustomBtn();
//retVal = CallWindowProc(oldWndProc, this.Handle, msg, wParam, lParam);
break;
}
return IntPtr.Zero;
}

private void Execute()
{
//do something
}

public void DrawCustomBtn()
{
try
{
IntPtr hwnd = FindWindow("HHTaskBar", null);
if (!hwnd.Equals(IntPtr.Zero))
{
IntPtr hDC = GetWindowDC(hwnd);
Graphics g = Graphics.FromHdc(hDC);
g.DrawImage((Bitmap)resManager.GetObject("icon_upper_right"), this.Width - ((Bitmap)resManager.GetObject("icon_upper_right")).Width - 4, 4);
g.Dispose();
ReleaseDC(hwnd, hDC);
}

}
catch (DllNotFoundException dllex)
{
throw dllex;
}
catch (Exception ex)
{
throw ex;
}
}

public void OnClosing(object sender, System.ComponentModel.CancelEventArgs e)
{

}

protected override void OnResize(EventArgs e)
{
base.OnResize(e);
try
{
if (Microsoft.WindowsCE.Forms.SystemSettings.ScreenOrientation != Microsoft.WindowsCE.Forms.ScreenOrientation.Angle0)
Microsoft.WindowsCE.Forms.SystemSettings.ScreenOrientation = Microsoft.WindowsCE.Forms.ScreenOrientation.Angle0;
}
catch (Exception ex)
{
Log.WriteInfoLog("RESIZING : rotation failed in : " + this.Name + " Message: " + ex.Message );
}
}
#endregion
}