const
  cOldDesktopName = 'Default';
  cNewDesktopName = 'Pokus';

procedure TForm1.FormDestroy(Sender: TObject);
begin
  CloseDesk(OldD);
  CloseDesk(NewD);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  OldD := OpenDesk(cOldDesktopName);
  NewD := OpenDesk(cNewDesktopName);
  if NewD = 0 then
    NewD := CreateDesk(cNewDesktopName);

  CurrentD := GetDeskName(GetCurrentDesk);
  if CurrentD = cOldDesktopName then
    bSwitchToOldD.Enabled := False
  else
    bSwitchToNewD.Enabled := False;
end;

procedure TForm1.bSwitchToOldDClick(Sender: TObject);
begin
  SetLastError(0);
  if SwitchDesk(OldD) then
    Close
  else
    Label4.Caption := 'Cannt switch to ' + IntToStr(OldD) + #13#10 +
      SysErrorMessage(GetLastError);
end;

procedure TForm1.bSwitchToNewDClick(Sender: TObject);
begin
  StartOnDesk(paramstr(0), '', cNewDesktopName);
  SwitchDesk(NewD);
end;

unit DesktopUtils;

interface

uses
  Windows, SysUtils;

function CreateDesk(Name: string): HDESK;
function OpenDesk(Name: string): HDESK;
function SwitchDesk(Desk: HDESK): Boolean;
function CloseDesk(Desk: HDESK): Boolean;
function GetCurrentDesk: HDESK;
function GetDeskName(Desk: HDESK): string;
function StartOnDesk(ApplicationName, CommandLine, DeskName: string): Boolean;

implementation

function CreateDesk(Name: string): HDESK;
var
  sa:_SECURITY_ATTRIBUTES;
begin
  FillChar(sa, SizeOf(sa), 0);
  sa.nLength:= sizeof(sa);
  sa.lpSecurityDescriptor:= Nil;
  sa.bInheritHandle:= True;

  Result := CreateDesktop(PChar(Name), Nil, Nil, 0, GENERIC_ALL, @sa);
end;

function OpenDesk(Name: string): HDESK;
begin
  Result := OpenDesktop(PChar(Name), 0, True, GENERIC_ALL);
end;

function SwitchDesk(Desk: HDESK): Boolean;
begin
  Result := SwitchDesktop(Desk);
end;

function CloseDesk(Desk: HDESK): Boolean;
begin
  Result := CloseDesktop(Desk);
end;

function GetCurrentDesk: HDESK;
var
  thr: Integer;
begin
  thr := GetCurrentThreadId;
  Result := GetThreadDesktop(thr);
end;

function GetDeskName(Desk: HDESK): string;
var
  buf: PChar;
  needed: Cardinal;
begin
  buf := AllocMem(1024);
  if not GetUserObjectInformation(Desk, UOI_NAME, buf, 1024, needed) then
  begin
    FreeMem(buf);
    buf := AllocMem(needed);
    GetUserObjectInformation(Desk, UOI_NAME, buf, needed, needed);
  end;
  Result := buf;
  FreeMem(buf);
end;

function StartOnDesk(ApplicationName, CommandLine, DeskName: string): Boolean;
var
  sa:_SECURITY_ATTRIBUTES;
  sti:STARTUPINFO;
  pri:_PROCESS_INFORMATION;
begin
  FillChar(sa, SizeOf(sa), 0);
  sa.nLength:= sizeof(sa);
  sa.bInheritHandle:= true;

  FillChar(sti, SizeOf(sti), 0);
  sti.cb:= SizeOf(sti);
  sti.lpDesktop:= PChar(DeskName);
  sti.dwFillAttribute:= FOREGROUND_BLUE;

  FillChar(pri, SizeOf(pri), 0);

  Result := CreateProcess(PChar(ApplicationName), PChar(CommandLine), @sa,
    @sa, True, CREATE_SEPARATE_WOW_VDM, Nil, Nil, sti, pri);
end;

end.

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs;

type
  TForm1 = class(TForm)
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
    procedure FormCreate(Sender: TObject);
    procedure WMShowWindow(var Msg: TWMShowWindow); message WM_ShowWindow;
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

//Этот обработчик и избавит тебя от WIN+D
procedure TForm1.WMShowWindow(var Msg: TWMShowWindow);
begin
  if not Msg.Show then
    Msg.Result := 0
  else
    inherited;
end;

procedure TForm1.FormCreate(Sender: TObject);
var
  HTaskbar: HWND;
  OldVal: LongInt;
begin
  try
    HTaskBar := FindWindow('Shell_TrayWnd', nil);
    SystemParametersInfo(97, Word(True), @OldVal, 0);
    EnableWindow(HTaskBar, False);
    ShowWindow(HTaskbar, SW_HIDE);
  finally
    with Form1 do
      begin
      BorderStyle := bsNone;
      FormStyle  := fsStayOnTop;
      Left        := 0;
      Top        := 0;
      Height      := Screen.Height;
      Width      := Screen.Width;
    end;
  end
end;

procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
var
  HTaskbar: HWND;
  OldVal: LongInt;
begin
  HTaskBar := FindWindow('Shell_TrayWnd', nil);
  SystemParametersInfo(97, Word(False), @OldVal, 0);
  EnableWindow(HTaskBar, True);
  ShowWindow(HTaskbar, SW_SHOW);
end;

end.

procedure TForm1.FormCreate(Sender: TObject);
var
  HTaskbar: HWND;
  OldVal: LongInt;
begin
  try
    HTaskBar := FindWindow('Shell_TrayWnd', nil);
    SystemParametersInfo(97, Word(True), @OldVal, 0);
    EnableWindow(HTaskBar, False);
    ShowWindow(HTaskbar, SW_HIDE);
  finally
    with Form1 do
      begin
      BorderStyle := bsNone;
      FormStyle  := fsStayOnTop;
      Left        := 0;
      Top        := 0;
      Height      := Screen.Height;
      Width      := Screen.Width;
    end;
  end
end;

procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
var
  HTaskbar: HWND;
  OldVal: LongInt;
begin
  HTaskBar := FindWindow('Shell_TrayWnd', nil);
  SystemParametersInfo(97, Word(False), @OldVal, 0);
  EnableWindow(HTaskBar, True);
  ShowWindow(HTaskbar, SW_SHOW);
end;

  TfmMain = class(TForm)
  ...
  private
    { Private declarations }
  protected
    procedure WMSysCommand(var Message:TWMSysCommand);message WM_SYSCOMMAND;
  public
    { Public declarations }
  end;


procedure TfmMain.WMSysCommand(var Message:TWMSysCommand);
begin
  if ((Message.CmdType and $FFF0) = SC_RESTORE) or
    ((Message.CmdType and $FFF0) = SC_MOVE) or
    ((Message.CmdType and $FFF0) = SC_MINIMIZE) then Message.Msg:=0
  else inherited;
end;