403 for folder

Hi, When i try to access any folder of my hosted site i get 403 (forbidden),but i want to show 404(file not found) as security measure. For ex. http://abcd:1234/mysite/images will display 403. My application is in ASP.NET 2.0 and IIS 6.0 . I have tried changing custom error in IIS but that only changes display,still in response header it send 403.I even tried custom error in web.config, httphandler only work for file not directory .So let me know if there is any way to achieve this.I read that ISAPI filter can do that but i havent got any such filter and i dont know how to make ISAPi filter. Please let me know if there is any solution to it ...