Well, after a bit of playing I've got something working now, I'm no Win32 coder but this seems to work:

using System;

using System.Drawing;

using System.Drawing.Imaging;

using System.Collections;

using System.ComponentModel;

using System.Windows.Forms;

using System.Data;

using mshtml;

using System.Runtime.InteropServices;

using Microsoft.Win32;

namespace ThumbMaker

{

/// <summary>

/// Summary description for Form1.

/// </summary>

public class Form1 : System.Windows.Forms.Form

{

private AxSHDocVw.AxWebBrowser axWebBrowser1;

/// <summary>

/// Required designer variable.

/// </summary>

private System.ComponentModel.Container components = null ;

private const string urlStr = "http://news.bbc.co.uk/" ;

public Form1()

{

//

// Required for Windows Form Designer support

//

InitializeComponent();

object o = null ;

this .Visible= false ;

axWebBrowser1.Navigate(urlStr, ref o, ref o, ref o, ref o);

}

const int WM_PAINT = 0x000F;

const int WM_PRINTCLIENT = 0x0318;

const int WM_ERASEBKGND = 0x0014;

const int WM_PRINT = 0x0317;

const int PRF_CHILDREN = 0x00000010;

const int PRF_CLIENT = 0x00000004;

public void GrabWindow()

{

IntPtr hWnd = this .Handle;

IntPtr hBmp;

Bitmap MyBitmap= null ;

IntPtr hDCMem = GDI32.CreateCompatibleDC((IntPtr) null );

IntPtr hDC = User32.GetWindowDC(hWnd);

hBmp = GDI32.CreateCompatibleBitmap(hDC,(IntPtr)axWebBrowser1.Width ,(IntPtr)axWebBrowser1.Height);

User32.ReleaseDC(hWnd, hDC);

IntPtr hOld = GDI32.SelectObject(hDCMem, hBmp);

User32.SendMessage(hWnd, WM_PRINT, hDCMem, new IntPtr(PRF_CLIENT | PRF_CHILDREN));

GDI32.SelectObject(hDCMem, hOld);

GDI32.DeleteObject(hDCMem);

MyBitmap = Bitmap.FromHbitmap(hBmp);

MyBitmap.Save( "test.png" ,ImageFormat.Png);

this .Close();

}

/// <summary>

/// Clean up any resources being used.

/// </summary>

protected override void Dispose( bool disposing )

{

if ( disposing )

{

if (components != null )

{

components.Dispose();

}

}

base .Dispose( disposing );

}

#region Windows Form Designer generated code

/// <summary>

/// Required method for Designer support - do not modify

/// the contents of this method with the code editor.

/// </summary>

private void InitializeComponent()

{

System.Resources.ResourceManager resources = new System.Resources.ResourceManager( typeof (Form1));

this .axWebBrowser1 = new AxSHDocVw.AxWebBrowser();

((System.ComponentModel.ISupportInitialize)( this .axWebBrowser1)).BeginInit();

this .SuspendLayout();

//

// axWebBrowser1

//

this .axWebBrowser1.Dock = System.Windows.Forms.DockStyle.Fill;

this .axWebBrowser1.Enabled = true ;

this .axWebBrowser1.Location = new System.Drawing.Point(0, 0);

this .axWebBrowser1.OcxState = ((System.Windows.Forms.AxHost.State)(resources.GetObject( "axWebBrowser1.OcxState" )));

this .axWebBrowser1.Size = new System.Drawing.Size(1024, 768);

this .axWebBrowser1.TabIndex = 0;

this .axWebBrowser1.DocumentComplete += new AxSHDocVw.DWebBrowserEvents2_DocumentCompleteEventHandler( this .axWebBrowser1_DocumentComplete);

//

// Form1

//

this .AutoScale = false ;

this .AutoScaleBaseSize = new System.Drawing.Size(5, 13);

this .ClientSize = new System.Drawing.Size(1024, 768);

this .Controls.Add( this .axWebBrowser1);

this .FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;

this .Name = "Form1" ;

this .ShowInTaskbar = false ;

this .Text = "Form1" ;

((System.ComponentModel.ISupportInitialize)( this .axWebBrowser1)).EndInit();

this .ResumeLayout( false );

}

#endregion

/// <summary>

/// The main entry point for the application.

/// </summary>

[STAThread]

static void Main()

{

Application.Run( new Form1());

}

private void axWebBrowser1_DocumentComplete( object sender, AxSHDocVw.DWebBrowserEvents2_DocumentCompleteEvent e)

{

GrabWindow();

}

}

class GDI32

{

[DllImport( "GDI32.dll" )]

public static extern bool BitBlt(IntPtr hdcDest,IntPtr nXDest,IntPtr nYDest,

IntPtr nWidth,IntPtr nHeight,IntPtr hdcSrc,

IntPtr nXSrc,IntPtr nYSrc,IntPtr dwRop);

[DllImport( "GDI32.dll" )]

public static extern IntPtr CreateCompatibleBitmap(IntPtr hdc,IntPtr nWidth,

IntPtr nHeight);

[DllImport( "GDI32.dll" )]

public static extern IntPtr CreateCompatibleDC(IntPtr hdc);

[DllImport( "GDI32.dll" )]

public static extern bool DeleteDC(IntPtr hdc);

[DllImport( "GDI32.dll" )]

public static extern bool DeleteObject(IntPtr hObject);

[DllImport( "GDI32.dll" )]

public static extern IntPtr GetDeviceCaps(IntPtr hdc,IntPtr nIndex);

[DllImport( "GDI32.dll" )]

public static extern IntPtr SelectObject(IntPtr hdc,IntPtr hgdiobj);

}

class User32

{

[DllImport( "User32.dll" )]

public static extern IntPtr GetDesktopWindow();

[DllImport( "User32.dll" )]

public static extern IntPtr GetWindowDC(IntPtr hWnd);

[DllImport( "User32.dll" )]

public static extern IntPtr ReleaseDC(IntPtr hWnd,IntPtr hDC);

[DllImport( "User32.dll" )]

public static extern int SendMessage(IntPtr hWnd, int Msg, IntPtr wParam, IntPtr lParam);

}

}