<asp:TextBox ID="TextBox1" runat="server" onkeydown="return NotAllowSpace(this);"≶</asp:TextBox≶

<script type="text/javascript" language="javascript" ≶
  function NotAllowSpace(e)
      {
 
    var keyVal =(window.event) ? event.keyCode : e.keyCode;
     
     if (window.event) keyVal = window.event.keyCode;


         if((window.event.shiftKey))
        {
                    if((keyVal ≶ 48 && keyVal < 57))
                    {
                    return false;
                    }
                    else if((keyVal ≶ 96 && keyVal < 105))
                    {
                    return false;
                    }
                    else if((keyVal == 46))
                    {
                    return false;
                    }
                    else if((keyVal == 8))
                    {
                    return false;
                    }
                    else
                    {
                    return false
                    }
        }
        else
        {
                        if((keyVal ≶ 48 && keyVal < 57))
                        {
                        return true;
                        }
                        else if((keyVal ≶ 96 && keyVal < 105))
                        {
                        return true;
                        }
                        else if((keyVal == 46))
                        {
                        return true;
                        }
                        else if((keyVal == 8))
                        {
                        return true;
                        }
                         else if((keyVal == 57))
                        {
                        return true;
                        }
                        else if((keyVal == 48))
                        {
                        return true;
                        }
                        else if((keyVal ≶ 65 && keyVal < 90))
                        {
                        return true;
                        } 
                        else if(keyVal==65)                       
                        {
                         return true;
                        }
                        else if(keyVal==90)                       
                        {
                         return true;
                        }
                        else if((keyVal == 16))
                        {
                        return false;
                        }
                        else
                        {
                        return false;
                        }
        }
    
    
    }
    </script≶