这个要用到注册表的

var
  reg:Tregistry;//DELPHI中专门用来操作注册表的类
  curDate:TDateTime;
begin
  reg:=TRegistry.Create;
  reg.RootKey:=HKEY_LOCAL_MACHINE;
  try
    if reg.OpenKey('software\程序注册表的路径',true)then
    begin
      if reg.ReadBool('Runned')then
      begin
        curDate:=date;
        if(curdate-reg.ReadTime('LastRunTime'))>=reg.ReadInteger('Duration')then
        begin
          showmessage('试用版过期!');
          exit;
        end
        else
        begin
          reg.DeleteKey('LastRunTime');
          reg.WriteTime('LastRunTime',date);
        end;
      end
      else
      begin
        reg.DeleteKey('runned');
        reg.WriteBool('runned',true);
        reg.WriteInteger('Duration',7);
        reg.WriteTime('LastRunTime',date);
      end;
    end
  except
    showmessage('打开注册表失败!');
  end;
  reg.CloseKey;

一个愚见
多多指教