uses
{$IFDEF WIN32}
  Registry; {We will get it from the registry}
{$ELSE}
  IniFiles; {We will get it from the win.ini file}
{$ENDIF}

{$IFNDEF WIN32}
const
  MAX_PATH = 144;
{$ENDIF}

function GetProgramAssociation(Ext: string): string;
var
{$IFDEF WIN32}
  reg: TRegistry;
  s: string;
{$ELSE}
  WinIni: TIniFile;
  WinIniFileName: array[0..MAX_PATH] of char;
  s: string;
{$ENDIF}
begin
{$IFDEF WIN32}
  s := '';
  reg := TRegistry.Create;
  reg.RootKey := HKEY_CLASSES_ROOT;
  if reg.OpenKey('.' + ext + '\shell\open\command',
    false) <> false then
  begin
    {The open command has been found}
    s := reg.ReadString('');
    reg.CloseKey;
  end
  else
  begin
    {perhaps thier is a system file pointer}
    if reg.OpenKey('.' + ext,
      false) <> false then
    begin
      s := reg.ReadString('');
      reg.CloseKey;
      if s <> '' then
      begin
        {A system file pointer was found}
        if reg.OpenKey(s + '\shell\open\command',
          false) <> false then
          {The open command has been found}
          s := reg.ReadString('');
        reg.CloseKey;
      end;
    end;
  end;
  {Delete any command line, quotes and spaces}
  if Pos('%', s) > 0 then
    Delete(s, Pos('%', s), length(s));
  if ((length(s) > 0) and
    (s[1] = '"')) then
    Delete(s, 1, 1);
  if ((length(s) > 0) and
    (s[length(s)] = '"')) then
    Delete(s, Length(s), 1);
  while ((length(s) > 0) and
    ((s[length(s)] = #32) or
    (s[length(s)] = '"'))) do
    Delete(s, Length(s), 1);
{$ELSE}
  GetWindowsDirectory(WinIniFileName, sizeof(WinIniFileName));
  StrCat(WinIniFileName, '\win.ini');
  WinIni := TIniFile.Create(WinIniFileName);
  s := WinIni.ReadString('Extensions',
    ext,
    '');
  WinIni.Free;
  {Delete any command line}
  if Pos(' ^', s) > 0 then
    Delete(s, Pos(' ^', s), length(s));
{$ENDIF}
  result := s;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  ShowMessage(GetProgramAssociation('gif'));
end;